I'm having the exact same problem. Mine was working fine and then one day when I tried to play a project I got "Guitar Tracks has stopped working and needs to close, etc". Since then it will occasionally play or even record, but usually I get the error message. It seems very strange since it will work sometimes (though very rarely) and not others.
It happened right after a Windows update, but that could be a coincidence. I've tried it with Guitar Tracks Pro and GTP3 with identical results. Could it be a RAM issue? (although I've checked to see how much is being used and it doesn't spike significantly when GTP is running) I have 4 gigs, all which the computer apparently sees...
Any insight into this problem would be tremendously appreciated. It's been driving me crazy for months!
-Mike