Drive mapping lost

Hello there! I have an annoyance that started minor but is now becoming a
real problem. The computers on our network have been randomly losing their
drive mappings. They are set up to automatically load via script file and do
so on most computers. The user has full access once mapped manually. This
is only happening to XP machines and our network uses server 2003. We have
looked into timeout issues and that is not it as well as power settings on
the affected users but that doesnt appear to be the problem either.
Typically something as simple as a logoff/logon corrects the problem but not
always. Any ideas what could be the problem and how to correct it??????

-- Jeremy Mcgee