FIRST AMENDMENT TO AMENDED AND RESTATED STOCKHOLDERS' AGREEMENT

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Exhibit 10.5.1

FIRST AMENDMENT
TO
AMENDED AND RESTATED STOCKHOLDERS' AGREEMENT

        THIS FIRST AMENDMENT TO AMENDED AND RESTATED STOCKHOLDERS' AGREEMENT (this "Amendment") is made and entered into effective April 8, 1999, by and among PROS Strategic Solutions, Inc., a Delaware corporation (the "Company"), and the undersigned holders of a majority of the total number of shares of Common Stock held by the Investors, the Founding Stockholders and the Stockholders. Capitalized terms used and not defined herein have the same meaning ascribed to them in the Agreement (as hereinafter defined).

W I T N E S S E T H:

        WHEREAS, the Company, the Investors, the Founding Stockholders, and the Stockholders entered into that certain Amended and Restated Stockholders' Agreement dated effective June 8, 1998 (the "Agreement");

        WHEREAS, Section 4.6 of the Agreement provides that the Agreement may be amended from time to time by an instrument in writing signed by the Company and the holders of a majority of the total number of shares of Common Stock held by the Investors, the Founding Stockholders, and the Stockholders, provided, however, that no amendment shall impose any additional material obligation on the Investors, the Founding Stockholders or any Stockholder without that party's written consent to such amendment;

        WHEREAS, the parties to this Amendment (other than the Company) are the holders of a majority of the total number of shares of Common Stock held by the Investors, the Founding Stockholders, and the Stockholders; and

        WHEREAS, the parties to this Amendment wish to amend the Agreement as hereinafter provided;

        NOW, THEREFORE, in consideration of the premises and other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree as follows:

        1.     The Agreement is hereby amended to add a new Section 4.16 which reads in its entirety as follows:

        "4.16    " Termination of Employee Stockholder's Rights and Obligations ."    Notwithstanding anything contained in this Agreement to the contrary, if an Employee Stockholder shall for any reason cease to be an officer or employee of the Company, the rights and obligations of the parties hereto under this Agreement with respect to such Employee Stoc