Hi, Chris, and Welcome.
Couple (OK, several)questions....
Where is this Error coming from? Is it from Windows? Is it from the Mac OS? Is it from the Windows version of Quickbooks?
What version of OSX are you running? (i.e. 10.4.11, 10.5.2, etc)
You mention the My Documents folder being Mirrored, so I assume you're using Fusion 2.0, yes?
Correct me if I'm wrong, but I cannot determine from your post...
Are you getting the problem when asking QB to open the file, or does it just toss it's cookies on launch, trying to auto-open it? Can you SEE the file if you navigate to it?
Also, where did this Virtual Machine come from? Converted from "some other form"? Built with Fusion? Boot Camp Partition?
Can you open from/save to the Shared z:\ drive using any OTHER application in Windows, i.e. Text Edit? (Is it only QuickBooks that's sad?)
While I'm on THAT track, will QB let you create a new Company or File (or whatever it is in your version, I use QBPro) ON that shared drive? (Just as a test?)
Thanks,
-art