Strange GUI Issue

This is a strange one that has only started happening after the update to 6.0.5.
All the GUI’s freeze. Cubase keeps working and you can delete each plugin gui but you cannot get them back. You can save but eventually have to shut down as eventually nothing works.
The only plugins I have been using are tried and tested with previous versions.
This seems to happen when I am listening to something on a loop and I have not issued any commands.

PC i7 intel 3.2 x 6
Windows 7 64 bit
12 Gig RAM
Fireface UC
Cubase 6.0.5
UAD 1 x2
UAD 2 Solo x1

It also trashed my preference - asked me to register - no projects upon loading -
all mixer windows needed to be reset to always on top.
Cubase does not seem to be as stable.

Had another crash.
What is really annoying is that it resets the mixer/load up prefs each time.
I really would appreciate some help here - especially as there is no real Steinberg support.