Shared drives on Vista stop responding...

[cross]

Having a problem with a Vista SP1 (32bit) computer. It has a few shared drives that are used on a LAN which are hosted on this Vista box. After about 24 hours, the shared drives stop responding. If I try to go to \\computername\ to see the drives on another computer (xp or vista) it just sits with an hour glass, then says device not found after some time (EDIT: I think its 'the network path was not found' not device, sorry). The computer is online, responds to a ping, and if I do the same thing (\\computername\) on the local machhine, the drives list themselves. The computer is not set to sleep or turn off the Hard Drive, or hibernate, only to turn off the monitor. Heres the really odd part: Restarting the computer fixes the issue, but, if I hit \\computername\ on another computer, then go and restart the Vista machine, as soon as the logoff process starts, the drives come up and list on the remote box. Its almost like theres some service hanging up, and when its forced closed at the shutdown, the network sharing kicks back in. Once the computer comes back up, all is normal again, for about 24 more hours.

Nothing in the event log showing any problems.
Tried flushing/registering DNS, no change.
Tried disabling/re-enabling network card, no change.
Tried repairing network connection, no change.

We did experience this issue on pre-sp1 vista machines, but this one has sp1, latest drivers, and latest bios update.

Has anyone else experienced this issue? Any ideas for troubleshooting this issue? I have checked and re-checked for spyware/malware, but nothing seems different on this unit then any others we have.