I am having the same issue. My Aero themes have seemingly all started this black bar thing as well. I have run the recommended sfc /scannow and have had no luck resolving the issue with that tool. As mmstone is claiming, I am only seeing this on the Aero themes. I have swapped to the Windows 7 Basic theme for usability now, not the windows classic.
I am not sure what I could have done, this appeared out of the blue this week. I do notice that we are both running 64 bit Pro, that may be helpful as a common link. I have never used any downloaded themes, the theme I set up was based on the windows aero theme, the only thing I had changed was the backgrounds, I had set those to a random 15 minute changing photo. That was all I have really ever changed on my theme, and I suddenly am having this issue.