Screen anomaly after 11.10 upgrade

My configuration:
      Pogo Altura M3
      AMD Athlon(tm) II X3 450 Processor
      nVidia Corporation GF108 [GeForce GT 430] [10de:0de1] (rev a1)
      Dell 15-in. flat screen monitor, Model Number E151FPb
      Ubuntu 11.10
      Ubuntu configuration at logon (matrix form of workspaces, i.e., with rows and columns -- set to 8 X 8)

Problem: An orange semi-transparent box appears at random times over right half screen, left half screen, or entire screen.

Observations:
      - anomaly began appearing after installation of 11.10 upgrade
      - after 11.10 upgrade, had to re-install the proprietary nVidia driver to make the Ubuntu desktop work again
      - anomaly was never observed under 11.04
      - box covers most of screen including launcher but excluding the top bar
      - box has bright orange border
      - box remains present when viewing one workspace or when entire matrix of workspaces is being viewed
      - anomaly usually appears after using the computer for a while (maybe an hour), but never immediately on initial boot and logon
      - box sometimes disappears after a few seconds or minutes
      - box sometimes disappears after clicking on another workspace
      - sometimes box will not disappear at all except by logging off and on
      - cannot make box appear at will
      - have screens shots of the various anomalies
      - presence of box does not seem to affect any software functionality (other than screen readability) but is distracting
      - anomaly does not appear with Ubuntu 2D selected at logon
      - anomaly not affected by number of work spaces

I scanned the existing questions and FAQs, but did not find anything similar to my problem. I do have screen shots of the anomaly.

Thanks for your help.