PO's being deleted in Vantage 6.1

Does anyone know what would cause po's to be deleted if the user says
they did not delete them? Is there a log file somewhere that would
show every po number created even if that po number has been deleted?
We also run MRP nightly and wondering if that would cause this?

Dan Ernst
Computer Services
Correct Craft, Inc.
(407) 855-4141