STOCK PURCHASE AGREEMENT

Exhibit 10.22

STOCK PURCHASE AGREEMENT

THIS STOCK PURCHASE AGREEMENT is entered into as of May 23, 2002 by NBT TECHNOLOGY, INC., a Delaware corporation (the “Company”), and STEVEN MCCANNE (the “Purchaser”).

SECTION 1. ACQUISITION OF SHARES.

(a) Transfer. On the terms and conditions set forth in this Agreement, the Company agrees to sell to the Purchaser, and Purchaser agrees to purchase, 5,000,000 Shares. The sale and purchase shall occur at the offices of the Company on the date set forth above or at such other place and time as the parties may agree.

(b) Consideration. The Purchaser agrees to pay $0.001 for each Purchased Share. The total Purchase Price is agreed to be at least 100% of the Fair Market Value of the Purchased Shares. Payment shall be made on the transfer date in cash or cash equivalents.

(c) Fully Vested. All Purchased Shares shall be fully vested.

(d) Defined Terms. Capitalized terms not defined above are defined in Section 9 of this Agreement.

SECTION 2. RIGHT OF FIRST REFUSAL.

(a) Right of First Refusal. In the event that the Purchaser proposes to sell, pledge or otherwise transfer to a third party any Purchased Shares, or any interest in Purchased Shares, the Company shall have the Right of First Refusal with respect to all (and not less than all) of such Purchased Shares. If the Purchaser desires to transfer Purchased Shares, the Purchaser shall give a written Transfer Notice to the Company describing fully the proposed transfer, including the number of Purchased Shares proposed to be transferred, the proposed transfer price, the name and address of the proposed Transferee and proof satisfactory to the Company that the proposed sale or transfer will not violate any applicable federal or state securities laws. The Transfer Notice shall be signed both by the Purchaser and by the proposed Transferee and must constitute a binding commitment of both parties to the transfer of the Purchased Shares. The Company shall have the right to purchase all, and not less than all, of the Purchased Shares on the terms of the proposal described in the Transfer Notice (subject, however, to any change in such terms permitted under Subsection (b) below) by delivery of a notice of exercise of the Right of First Refusal within 30 days after the date when the Transfer Notice was received by the Company.

(b) Transfer of Shares. If the Company fails to exercise its Right of First Refusal within 30 days after receiving the Transfer Notice, the Purchaser may, not later than 90 days after the Company received the Transfer Notice, conclude a transfer of the Purchased Shares subject to the Transfer

Notice on the terms and conditions described in the Transfer Notice, provided that any such sale is made in compliance with applicable federal and state securities laws and not in violation of any other contractual restrictions to which the Purchaser is bound. Any proposed transfer on terms and conditions different from those described in the Transfer Notice, as well as any subsequent proposed transfer by the Purchaser, shall again be subject to the Right of First Refusal and shall require compliance with the procedure described in Subsection (a) above. If the Company exercises its Right of First Refusal, the parties shall consummate the sale of the Purchased Shares on the terms set forth in the Transfer Notice within 60 days after the Company received the Transfer Notice (or within such longer period as may have been specified in the Transfer Notice); provided, however, that in the event the Transfer Notice provided that payment for the Purchased Shares was to be made in a form other than cash or cash equivalents paid at the time of transfer, the Company shall have the option of paying for the Purchased Shares with cash or cash equivalents equal to the present value of the consideration described in the Transfer Notice.

(c) Additional or Exchanged Securities and Property. In the event of a merger or consolidation of the Company with or into another entity, any other corporate reorganization, a stock split, the declaration of a stock dividend, the declaration of an extraordinary dividend payable in a form other than stock, a spin-off, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities, any securities or other property (including cash or cash equivalents) that are by reason of such transaction exchanged for, or distributed with respect to, any Purchased Shares subject to this Section 2 shall immediately be subject to the Right of First Refusal. Appropriate adjustments to reflect the exchange or distribution of such securities or property shall be made to the number and/or class of the Purchased Shares subject to this Section 2.

(d) Termination of Right of First Refusal. Any other provision of this Section 2 notwithstanding, in the event that the Stock is readily tradable on an established securities market when the Purchaser desires to transfer Purchased Shares, the Company shall have no Right of First Refusal, and the Purchaser shall have no obligation to comply with the procedures prescribed by Subsections (a) and (b) above.

(e) Permitted Transfers. This Section 2 shall not apply to (i) a transfer by beneficiary designation, will or intestate succession or (ii) a transfer to one or more members of the Purchaser’s Immediate Family or to a trust established by the Purchaser for the benefit of the Purchaser and/or one or more members of the Purchaser’s Immediate Family, provided in either case that the Transferee agrees in writing on a form prescribed by the Company to be bound by all provisions of this Agreement. In addition, this Section 2 shall not apply to the Purchaser’s transfer of up to an aggregate five percent (5%) of the Purchased Shares. If the Purchaser transfers any Purchased Shares, either under this Subsection (e) or after the Company has failed to exercise the Right of First Refusal, then this Agreement shall apply to the Transferee to the same extent as to the Purchaser.

(f) Termination of Rights as Stockholder. If the Company makes available, at the time and place and in the amount and form provided in this Agreement, the consideration for the Shares to be purchased in accordance with this Section 2, then after such time the person from whom such Shares are to be purchased shall no longer have any rights as a holder of such Shares (other than the right to receive payment of such consideration in accordance with this

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Agreement). Such Shares shall be deemed to have been purchased in accordance with the applicable provisions hereof, whether or not the certificate(s) therefor have been delivered as required by this Agreement.

(g) Assignment of Right of First Refusal. The Board of Directors may freely assign the Company’s Right of First Refusal, in whole or in part. Any person who accepts an assignment of the Right of First Refusal from the Company shall assume all of the Company’s rights and obligations under this Section 2.

SECTION 3. OTHER RESTRICTIONS ON TRANSFER.

(a) Purchaser Representations. In connection with the issuance and acquisition of Shares under this Agreement, the Purchaser hereby represents and warrants to the Company as follows:

(i) The Purchaser is acquiring and will hold the Purchased Shares for investment for his or her account only and not with a view to, or for resale in connection with, any “distribution” thereof within the meaning of the Securities Act.

(ii) The Purchaser understands that the Purchased Shares have not been registered under the Securities Act by reason of a specific exemption therefrom and that the Purchased Shares must be held indefinitely, unless they are subsequently registered under the Securities Act or the Purchaser obtains an opinion of counsel, in form and substance satisfactory to the Company and its counsel, that such registration is not required. The Purchaser further acknowledges and understands that the Company is under no obligation to register the Purchased Shares.

(iii) The Purchaser is aware of the adoption of Rule 144 by the Securities and Exchange Commission under the Securities Act, which permits limited public resales of securities acquired in a non-public offering, subject to the satisfaction of certain conditions, including (without limitation) the availability of certain current public information about the issuer, the resale occurring only after the holding period required by Rule 144 has been satisfied, the sale occurring through an unsolicited “broker’s transaction,” and the amount of securities being sold during any three-month period not exceeding specified limitations. The Purchaser acknowledges and understands that the conditions for resale set forth in Rule 144 have not been satisfied and that the Company has no plans to satisfy these conditions in the foreseeable future.

(iv) The Purchaser will not sell, transfer or otherwise dispose of the Purchased Shares in violation of the Securities Act, the Securities Exchange Act of 1934, or the rules promulgated thereunder, including Rule 144 under the Securities Act. The Purchaser agrees that he or she will not dispose of the Purchased Shares unless and until he or she has complied with all requirements of this Agreement applicable to the disposition of Purchased Shares and he or she

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has provided the Company with written assurances, in substance and form satisfactory to the Company, that (A) the proposed disposition does not require registration of the Purchased Shares under the Securities Act or all appropriate action necessary for compliance with the registration requirements of the Securities Act or with any exemption from registration available under the Securities Act (including Rule 144) has been taken and (B) the proposed disposition will not result in the contravention of any transfer restrictions applicable to the Purchased Shares under the securities laws or regulations of any state.

(v) The Purchaser has been furnished with, and has had access to, such information as he or she considers necessary or appropriate for deciding whether to invest in the Purchased Shares, and the Purchaser has had an opportunity to ask questions and receive answers from the Company regarding the terms and conditions of the issuance of the Purchased Shares.

(vi) The Purchaser is aware that his or her investment in the Company is a speculative investment that has limited liquidity and is subject to the risk of complete loss. The Purchaser is able, without impairing his or her financial condition, to hold the Purchased Shares for an indefinite period and to suffer a complete loss of his or her investment in the Purchased Shares.

(b) Securities Law Restrictions. Regardless of whether the offering and sale of Shares under this Agreement have been registered under the Securities Act or have been registered or qualified under the securities laws of any state, the Company at its discretion may impose restrictions upon the sale, pledge or other transfer of the Purchased Shares (including the placement of appropriate legends on stock certificates or the imposition of stop-transfer instructions) if, in the judgment of the Company, such restrictions are necessary or desirable in order to achieve compliance with the Securities Act, the securities laws of any state or any other law.

(c) Market Stand-Off. In connection with any underwritten public offering by the Company of its equity securities pursuant to an effective registration statement filed under the Securities Act, including the Company’s initial public offering, the Purchaser shall not directly or indirectly sell, make any short sale of, loan, hypothecate, pledge, offer, grant or sell any option or other contract for the purchase of, purchase any option or other contract for the sale of, or otherwise dispose of or transfer, or agree to engage in any of the foregoing transactions with respect to, any Purchased Shares without the prior written consent of the Company or its underwriters. Such restriction (the “Market Stand-Off”) shall be in effect for such period of time following the date of the final prospectus for the offering as may be requested by the Company or such underwriters. In no event, however, shall such period exceed 180 days. The Market Stand-Off shall in any event terminate two years after the date of the Company’s initial public offering. In the event of the declaration of a stock dividend, a spin-off, a stock split, an adjustment in conversion ratio, a recapitalization or a similar transaction affecting the Company’s outstanding securities without receipt of consideration, any new, substituted or additional securities that are by reason of such transaction distributed with respect to any Shares subject to the Market Stand-Off, or into which such Shares thereby become convertible, shall

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immediately be subject to the Market Stand-Off. In order to enforce the Market Stand-Off, the Company may impose stop-transfer instructions with respect to the Purchased Shares until the end of the applicable stand-off period. The Company’s underwriters shall be beneficiaries of the agreement set forth in this Subsection (c). This Subsection (c) shall not apply to Shares registered in the public offering under the Securities Act, and the Purchaser shall be subject to this Subsection (c) only if the directors and officers of the Company are subject to similar arrangements.

(d) Rights of the Company. The Company shall not be required to (i) transfer on its books any Purchased Shares that have been sold or transferred in contravention of this Agreement or (ii) treat as the owner of Purchased Shares, or otherwise to accord voting, dividend or liquidation rights to, any transferee to whom Purchased Shares have been transferred in contravention of this Agreement.

SECTION 4. SUCCESSORS AND ASSIGNS.

Except as otherwise expressly provided to the contrary, the provisions of this Agreement shall inure to the benefit of, and be binding upon, the Company and its successors and assigns and be binding upon the Purchaser and the Purchaser’s legal representatives, heirs, legatees, distributees, assigns and transferees by operation of law, whether or not any such person has become a party to this Agreement or has agreed in writing to join herein and to be bound by the terms, conditions and restrictions hereof.

SECTION 5. LEGENDS.

All certificates evidencing Purchased Shares shall bear the following legends:

“THE SHARES REPRESENTED HEREBY MAY NOT BE SOLD, ASSIGNED, TRANSFERRED, ENCUMBERED OR IN ANY MANNER DISPOSED OF, EXCEPT IN COMPLIANCE WITH THE TERMS OF A WRITTEN AGREEMENT BETWEEN THE COMPANY AND THE REGISTERED HOLDER OF THE SHARES (OR THE PREDECESSOR IN INTEREST TO THE SHARES). SUCH AGREEMENT GRANTS TO THE COMPANY CERTAIN RIGHTS OF FIRST REFUSAL UPON AN ATTEMPTED TRANSFER OF THE SHARES. THE SECRETARY OF THE COMPANY WILL UPON WRITTEN REQUEST FURNISH A COPY OF SUCH AGREEMENT TO THE HOLDER HEREOF WITHOUT CHARGE.”

“THE SHARES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD, PLEDGED, OR OTHERWISE TRANSFERRED WITHOUT AN EFFECTIVE REGISTRATION THEREOF UNDER SUCH ACT OR AN OPINION OF COUNSEL, SATISFACTORY TO THE COMPANY AND ITS COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED.”

If required by the authorities of any state in connection with the issuance of the Purchased Shares, the legend or legends required by such state authorities shall also be endorsed on all such certificates.

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SECTION 6. NOTICE.

Any notice required by the terms of this Agreement shall be given in writing. It shall be deemed effective upon (i) personal delivery, (ii) deposit with the United States Postal Service, by registered or certified mail, with postage and fees prepaid or (iii) deposit with Federal Express Corporation, with shipping charges prepaid. Notice shall be addressed to the Company at its principal executive office and to the Purchaser at the address that he or she most recently provided to the Company in accordance with this Section 6.

SECTION 7. ENTIRE AGREEMENT.

This Agreement constitutes the entire contract between the parties hereto with regard to the subject matter hereof. It supersedes any other agreements, representations or understandings (whether oral or written and whether express or implied) that relate to the subject matter hereof.

SECTION 8. CHOICE OF LAW.

This Agreement shall be governed by, and construed in accordance with, the laws of the State of California, as such laws are applied to contracts entered into and performed in such state.

SECTION 9. DEFINITIONS.

(a) “Agreement” shall mean this Stock Purchase Agreement.

(b) “Board of Directors” shall mean the Board of Directors of the Company, as constituted from time to time.

(c) “Fair Market Value” shall mean the fair market value of a Share, as determined by the Board of Directors in good faith. Such determination shall be conclusive and binding on all persons.

(d) “Immediate Family” shall mean any child, stepchild, grandchild, parent, stepparent, grandparent, spouse, sibling, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law or sister-in-law and shall include adoptive relationships.

(e) “Purchased Shares” shall mean the Shares purchased by the Purchaser pursuant to this Agreement.

(f) “Purchase Price” shall mean the dollar value for which one Share may be purchased pursuant to this Agreement, as specified in Section 1(b).

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(g) “Right of First Refusal” shall mean the Company’s right of first refusal described in Section 2.

(h) “Securities Act” shall mean the Securities Act of 1933, as amended.

(i) “Share” shall mean one share of Stock.

(j) “Stock” shall mean the Common Stock of the Company, with a par value of $0.0001 per Share.

(k) “Transferee” shall mean any person to whom the Purchaser has directly or indirectly transferred any Purchased Share.

(l) “Transfer Notice” shall mean the notice of a proposed transfer of Purchased Shares described in Section 2.

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IN WITNESS WHEREOF, each of the parties has executed this Stock Purchase Agreement, in the case of the Company by its duly authorized officer, as of the day and year first above written.

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