Mapped Drives Not Accessible

All,

I have Vista Ultimate (32-bit) installed with SP1 and all the latest
patches. The computer is in a Windows Server 2003 based Active Directory
domain. There is a GPO which mapps a number of drives via a logon script.
When I initially login to the domain, the logon script runs and all of the
drives are mapped and accessible. However, if i lock the PC or if it goes
into suspense mode, when i lo back in, the drives are inaccessible and I get
the following if I double-click on any of the mapped drives:

H:\ refers to a location that is unavailable. It could be on a hard drive
on this computer, or on a network. Check to make sure...

Any assistance would be appreciated.