I'm having an intermittant problem with a branch office's pop3 email access to a hosted server. It seems the people in this question were having the same problem only with exchange:
Every so often (once or twice a week) for an office of 6 people, excel or word document attachments will come in missing 100 or so bytes. Word or excel will say:
The document name or path is not valid. Try these suggestions.
*check the permissions for the document or drive
*Use the file open dialog box to locate the document.
If the sender resends the corrupt attachments they will come through fine.