It looks like this is a bug in Fusion 3. I’ve seen this exact issue on Fusion 3 with Windows 7 Ultimate. Here’s a VMware Community forum post with a temporary “work-around” until they release a fix for the bug.
The work-around is this, as verified from the Forum above. This worked for me in my tests, yet every so often I’m still having issues getting to some files as the path is still too long: “A quick workaround, which works in my tests is to shorten the paths to your files in your “Shared Folders” drive mappings.”