Mapped network drives sometimes show a big red X in Windows 7. When you open them with Explorer, all seems to work OK. But if you have to connect to them first with a program like Access that may be trying to connect to a database back-end you'll get a nasty error message, and the back-end won't connect.
The problem may be that Windows 7 attempts to connect the network drive before the network connection is established. Sounds like it could be a bug.
The work around is a registry entry (hack?) that you can implement with this handy .reg script. Just create a .reg file and put this text in it:
... then open it ("Merge" it) on each Windows 7 computer that has the problem. Reboot and all should connect OK.
A user reports that the above registry fix/hack did not resolve the problem. So I'm still looking for a way to get Windows 7 to reconnect network drives AFTER the network connection has been established. Can you help? Any ideas?