When a non-administrator is prompted by Vista’s UAC to enter Administrator credentials for security elevation, the program that then runs under Administrator priveleges will not have access to the logged in users mapped network drives.

For example, if Mike the user was to copy some files from the mapped network drive S: to C:Windows, he would be prompted by UAC to enter Administrative priveleges. So the Administrator John enters his details but then the copy fails because the network drive is no longer available now that the user is elevated.

This scenerio happens also when installing programs that require administrative priveleges during installation from a network drive.

To fix this, an administrator can make the following registry change,

You can also download and run this registry file to import the above change to your registry,
  EnableLinkedConnections.reg (134 bytes, 3,188 hits)