There's an article at MS that says if you try to open a file that's on a mapped drive and the program hangs, check all mapped drives. If one is not responding or temorarily disconnected, the application will hang.
http://support.microsoft.com/kb/313937/en-us
WORKAROUND
To work around this behavior, use one of the following methods.
Method 1: Do not use persistent connections
When you connect a mapped drive, click to clear the Reconnect at logon check box. By clearing this check box, the mapped drive will not be connected the next time that you log on to the computer. See the "More Information" section for more information about how to map a network drive.
Method 2: Use a user logon script
If you can, use a logon script to connect a user to the appropriate servers every time that the user logs on. Make sure that the script maps the drive in a non persistent state. If the drive is not available as the logon script runs, the drive is not mapped. This behavior prevents the issue.
Method 3: Use server mirroring
If the connection is over a Wide Area Network (WAN), consider implementing server mirroring. Server mirroring duplicates a distant server locally. Then, map your drive to the local, duplicate server. Doing this can reduce the wait time by connecting to a local server.
Method 4: Use a shortcut to the network location
Use a shortcut on the Microsoft Windows desktop or in My Network Places to connect to the network location that you want.