What Autodesk failed to mention is what may be the real cause of the issue is. In my experience I have been able to narrow it down to a conflict with a commonly used ASHRAE Duct Fitting Database utility. While the folks at Auodesk might not be reaching for this utility too often it is fairly common in the design industry to have both applications installed at the same time.
It seems that they both reference the same culprit ASHRAEDUCTDLL.dll binary. Based on the descriptions of the fix for the problem Windows registry gets confused when both applications are installed. I have since uninstalled the ASHRAE utility and run the fix quoted below from Inside the System and things are back to normal. Hopefully Autodesk fixes this issue in 2012 and patches it up for 2010 and 2011.
Try running this after uninstalling the ASHRAE utility if the removal alone doesn’t fix the problem.
- Click on Start, then Run
regsvr32 "C:Program FilesAutodeskRevit MEP 2011ProgramASHRAEDUCTDLL.dll"in the window
- Click OK