I have windows 7 64 bit

When I close DDO occasionally I get a graphics error on the top half of my screen. What basically happens is I get small multicolored squares popping up and disappearing. Logging off and back in fixes it so I am reasonably sure it isn't an overheating processor/graphics processor and there isn't anything running in the background except steam so I am rather befuddled as to what is causing it.

Any tips?