VM GUI Hangs but VM still running

I'm having a problem with Fusion 5 and OSX Server 10.6.8.

After the monitor is turned off (physically) leaving the machine running, when I turn the monitor back on the GUI for the VM is hung, though Fusion menus al work fine. 

I can log in to the VM via screen share from another computer and the VM is running, I can interact with it, shut it down and al other normal things, but the display on the host never updates.

What is even more weird is that once I have the screen sharing running I can also use the mouse and keyboard on the HOST to interact with the VM and see what is happening on the screen share. 

So, it's only the video output that's hung.

Any idea what could cause this and how I go about fixing it?

The host is a MacMini Server (2012) with 16GB ram running latest Mountain Lion Server.

The VM is 10.6.8 Server using 2 cores and 4096 ram.

Fusion is 5.0.3 (1040386)

Thanks!