Can't move one folder from external HD to internal HD
This unfortunately indicates a disk error...
I suggest digging up snapshots of previous virtual machines and seeing if you can restore the .pvm to one of those previous, working, versions.  Back up the VM somewhere first and maybe even fire it up to back up the data inside.

I would also look through the Console (Applications/Utilities/Console.app) to see if more disk I/O errors are being logged, because this is typically in my experience the first sign of a failing hard-drive.