The Gear fixes have luckily worked for me the one time I encountered this.
One quick thing that might be checked is the Windows system files (that was the solution in the Apple Windows iTunes thread below. ymmv). At administrator command prompt run sfc /scannow
There have been a couple of threads here and solutions with registry entries, but if anyone wants to pursue this further, there are a couple of threads at Microsoft and Apple (Windows iTunes) that seem to cover pretty much everything I’ve seen about this:
https://discussions.apple.com/thread/3585599?start=0&tstart=0