Make sure that the Cursor points on SABIN and NOT "Blitz" in his "fight menu". For example: Sabins ATB bar gets full, and Sabins menu is shown. Move the cursor to BLITZ and press X ONCE! The "Hand-Cursor" is now pointing at Sabin. Now, press use the Left-Right-Left-X combination with a brief 0.5 seconds pause between each time you press a button. That should do the trick.
Ha. I gave up on my comp and rented the GBA version. Still had trouble, and eventually I just started punching in left, right, left, right left, right, left and a over and over again. haha At least I got past it. Now I wont have to use Blitz ever again. >_<
Have you tried doing it SLOWLY. You don't have to do it fast at all. In fact, you can push left, then right, then go up, use the restroom, wash your hands, go to the kitchen and make yourself a sandwhich, then come back and push left again, then X.