Hmmmm, X-Copy...
Thomas mentioned earlier on in the thread that you might have virus
trouble and according to the latest Virus-Z brainfile there appears to
be versions of X-Copy that are viruses.
I know X-Copy is good for duplicating disks precisely (with Nibble
mode) but there were a lot of illegal versions of it floating around.
I seem to remember there being a green GUI and a pink one.
Be careful that one infected disk isn't spreading a virus through
memory to another. If you have doubt then switch the power off for 20
seconds (a reset warm reboot may not be sufficient to clear the memory
of viruses).
Other than that it could be just the drive head needs recalibrating or
cleaning up with a cleaner diskette.
Before you dump your drive though, let us know the exact make, model
and revision for future reference!
:-D