Actually, I had the same problem a while back. If I remember correctly, I think I installed the 32bit and 64bit VSTs in the same folder which cause everything to go wacky. You can try to reinstall AL4 and specify different folder for the 64bit VSTs (also, get rid of the other VSTs in the folder first)
As I said, I THINK that was the problem. If that doesn't work, write to Ableton and you should get a response (if you have the INTRO version at least)