APPLIES TO:

Symptoms

The Virtual Machine (VM) window is not visible after upgrade from Mac OS X Snow Leopard to Mac OS X Lion while the live screenshot in the Dock  and in the VM list  indicates that the VM is running.

Cause

Parallels Desktop for Mac 6 was running in another space prior to the Mac OS upgrade to Lion.

Resolution

1) Go to Applications on the Mac side and start Mission Control app:



 2)  Delete all spaces.
To delete a space you can hold the  ALT  button and press the cross.



 3)  Restart Parallels Desktop

 4 )  Start the Virtual Machine

Add removed Spaces if you like. The Virtual Machine window will appear in the 1st space.