You have to replace the cut scene movie to move forward (it's probably corrupted). You can take the cut scene from Vernon Roche way, rename it like the one from Iorveth and launch the game again. Once past the cut scene save your game and you can put back the original files. You have to replace the file `load_a2_a3_i.usm` with `load_a2_a3_r.usm`, renaming the last one like the first one.