Level 6 Guile? Stand L Punch > Stand M Punch? Press Light Punch (y), then press Medium Punch (x) close to your opponent. Make sure both punches connect (you only have a certain amount of time to input the second command) and that they hit your target. Blocked hits do not count. Got it almost immediatly. Nothing broken with this game, rest assured.
edit: you can find tons of documentation for the original Super Street Fighter IV. Everything you find there can be applied to the 3D Edition 1:1
That is really messed up because when I press the second button (x), it doesn't count for some reason.. I messed around with it for a while though, then it worked. Thanks