SONAR X1 Crashes when switching to another application

Hi,
My SONAR X1 Producer Expanded almost always crashes when I switch to Windows Explorer or another application.
This happens on both the 32 and 64 bit versions of X1.
This didn't use to happen, but I can't pinpoint what has changed. 
I re-installed Sonar - no dice.
I don't have much else open - just switching to OneNote or Windows Explorer will cause this. Especially Explorer.
 
Ideas?
 
Thanks,
Andrew
 
Windows 7 64 SP1 with an Intel I7, lotsa RAM. 
Line 6 UX2.