In the official blog, anime song singer HIMEKA
apologized to the fans and the staff for her behavior at ANIMAX live concert held on November 22nd in Osaka. While she was singing "Asu eno Kizuna" (the OP song of Valkyria Chronicles
), she forgot the lyrics and quit the stage in the middle of the show. She promised that she won't run away from the stage anymore.
Source: HIMEKA's official blog