My PC always locked up every time I tried use Eraser within a TrueCrypt volume. Then I realized that since the volume is already encrypted, the files inside don't need to be erased, they can just be deleted. I've never recovered anything forensically afterward, so the concept seems to be true.
The only way I could make it hang here was to manually go through Explorer (without having the TC volume - "My Volume" - mounted) and trying to either defrag or erase freespace on "My Volume" itself.
It won't do it - or if it will, I 've never left it trying long enough to find out.
What I finally wound up doing was using FolderHide on "My Volume", to take it out of the equation entirely unless I actually wanted to mount the volume in TC (at which time, I un-hide it, of course). Pete