Occasionally - but too, too often - a Fusion 6.0.2 VM refuses to close its window. Fusion displays the message: The virtual machine "Windows 7x64" is busy.
I click "OK" and try again. It's still "busy." I go to the Fusion menu and choose "Quit." The VM is still busy.
The only way I can shut down a VM caught in this is to go to OS X "Force Quit" and kill Fusion.
Typically I do a complete 'shutdown' of the guest OS. Even then the VM claims to be busy. But then I can Force Quit with a clearer conscience. This is annoying, and means that I have to shut down my VM before I can stop it.