Comment on the Alday-Maldacena solution in calculating scattering amplitude via AdS/CFT

Following the recent proposal of Alday and Maldacena to obtain the strong coupling scattering amplitude in N=4 SYM via AdS/CFT, we point out that a unique solution can be obtained by imposing all the Virasoro constraints. In the case of four-gluon scattering, this solution is identical to the Alday-Maldacena solution, which is in accordance with the ansatz of Bern, Dixon and Smirnov. This also solves the moduli space problem of the four-point solution in a recent paper of Mironov, Morozov and Tomaras.