Canon 10d and err99

Cycling through 3 Canon 10d bodies it was bound to happen to me eventually.  I was shooting about 2 weeks ago and my camera made what sounded like half of a shutter noise.  I looked at the LCD and there was "err99".  I did what I've read to do and turned the camera off, took off the lens, put the lens back on, and turned the camera back on and it worked flawlessly for the rest of the day.

Fast forward to Tuesday.  First shot out of the bag and I got the same error.  Turning it off and on would work for one shot, although I haven't looked at the images to see if it's even capturing anything. 

From what I've read this is usually an issue with non-Canon lenses, and I do use Sigma lenses.  So I switched to a 50mm Canon lens and had the same error.  Took the lens off - same error.

Any other suggestions of things I can try before I box this guy up and send it to Canon to get looked at?  (I'm typing this while waiting for the "10-20 minutes" with batteries removed to do a "hard reset").

Mike, Thanks for the suggestions.  Unfortunately I've tried all of that.  What worries me is that the error shows up even without a lens on the body.