If you turn on your log (console)check to see if you are seeing a hardware error that says "Verification Failed, Check Hardware!". I had a similar issue with a 6750 and it was a hardware issue/driver issue with guiminer worked fine with bitminter and eventually had to edit a config file to resolve to get guiminer working correctly, but not telling you to do that if it's not needed.
Thanks for the help, but I am going to use cgminer because of it's features.