At times like this, nothing beats a good backup.  In fact make a complete
backup of your database now and put it away for safe keeping.

Tony Toews has an excellent web page on database corruption.
http://www.granite.ab.ca/access/corruptmdbs.htm

Allen Brown also has excellent info on corruption.
http://allenbrowne.com/ser-47.html

I have a white paper in a Word document named Fix Corrupt Access Database
towards the bottom this page:
http://www.rogersaccesslibrary.com/OtherLibraries.asp

Are these databases on a network drive? If so I suspect a network problem
like a bad switch, router, or even a network card (NIC) that can be on a
computer not even using the databases! I suggest that your network people run
a sniffer to look for bad packets and other problems. Access would be a good
network stress testing tool as if there is a weakness, Access seems to find
it.