Well, maybe it wasn't meant that way, but it should work anyway.
Dazza, could you please try to identify the problematic file? I mean, it's probably caused by one (of just a few) file(s)... if you don't scan the whole C: drive but only some folder, you should be able to find its location (you can guess according to the area that was scanned right before the program crashed).
It's possible that (for example) the filename is too long (I have fixed this problem recently for avast! 4.5).