You didn't mention if the copy is after work hours or during work hours, but VFP database files can't be copied while being used.

http://www.tgrmn.com/web/forum/viewtopict255.htm

And I think I remember read something about DBFs not being compatible with SO shadow backups.

You may know that part of the DBF data is cached on clients, so corruption may occur if data is copied while used by clients.