SymptomsThe 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.
CauseParallels Desktop for Mac 6 was running in another space prior to the Mac OS upgrade to Lion.
Please perform the following steps: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.