Multiple Arduino Mega2560 and Windows 7 SP1

Up until very recently I could run 3 Arduino Mega 2560 R3s’ concurrently. They now detect/install intermittently and never all three at once. Sometimes one is detected as a Mega 2560 R3, sometimes two, but never 3. The Arduino boards will show up as “Unknown device” and the driver will not install with the usual manual process. I’m suspicious once my PC auto upgraded to the last mandatory Windows patch set the problem began. Install/detection may or may not occur successfully even on the same board! Any help would much appreciated I have a large Arduino and motor shield investment sitting idle.

Test Variations:

  1. Swapped out USB Cables
  2. Tried different PCs
  3. Swapped out Arduino boards
  4. Installed latest IDE and drivers. 1.0.3 and 1.0.2 exhibit same problem
  5. The RunOnce key is in the Registry.