Network Error when Run As Administrator from Shared Folder

I have a VPC 2007 running Windows 7 x86 on a Windows 7 x64 host system with
Virtual Machine Additions installed. The VHD is a differencing disk. I have
a Shared Folder (mapped to Z to my host system's primary drive set to
connect on every start. I can execute programs without any issues directly
from that Shared Folder, except when I attempt to execute those programs as
an administrator. When I do that - regardless of the file name, file type
(exe, bat) - it always reports a "Network Error", insisting that it "cannot
access Z:\<filename>". Allowing Windows 7 to diagnose/troubleshoot the issue
finds no problems.

I believe I had this same issue when the guest OS was Vista. The workaround
is to copy the program into the guest OS and run it from there.

Any ideas as to how to resolve this properly?