I just started getting this same error message out of the blue today.
Tried restoring the NTVDM files in windows XP, scanned for viruses (the WWW info suggested that).
Later discovered I could still compile other code for other PIC types (was using 12F675 initially). I then installed a second new and fresh copy of PBP and pointed MCS to compile from the new copy. No more error messages....

Looks like PBP or the Assembler was corrupted.

Cheers,
Martin