I had the same problem and just figured out how to fix it.
What caused the problem for me was that I moved a Windows 7 vm that I had initially built using Fusion 3 on a different MacBook - which coincidentally also had a different user account name (but that may not be a factor).
Each time I started the migrated Windows 7 VM or launched the Windows Explorer on the new MacBook, a window was displayed with the error "Windows cannot access
vmware-host\shared folders\desktop".
To fix the issue, while logged into the Windows 7 VM on the new MacBook, I went into the VM properties and removed all the Shared Folders that were set up for it - including the Mirroring settings for Desktop, Documents, Music and Pictures. This cuased my Windows 7 VM to automatically log me out of the session and re-login again. Once I relogged in, the errors were gone - but then of course were were also my mirrored settings.
So, I then had to recreate the mirrored/shared folders by just going back into the VM properties (while still logged into the same new Windows 7 session immediately following the previous removal effort) and selecting "Share Folders on your Mac" and selecting the mirrored folders I wanted again (e.g. Desktop, Documents, etc.). This once again automatically prompted me to log out of the current Windows 7 session in the VM... once I re-logged back in the shared folders and mirroring settings were working again as I wanted - still without the errors.
Hope this helps anyone with the same issue!
Cheers! -chris