Vista Mapped Drive Problem

Using(unfortunately) Windows Vista PC on a network of 5 XPcomputers and Sever 2003. We map a drive on the server(S. We attempt to load a program from the mapped drive which we have done without problems for years. The Windows Vista PC starts the install and then gives an error message saying we must run this from a mapped drive. The problem is that we ARE running it from a mapped drive. ???

Any thoughts or help would be greatly appreciated.

Thanks.