This error is like a catch all of anything that could go wrong in your 2010 Farm, especially after upgrade! There is a reason the 12 Hive is left over at the end of the upgrade. You have stuff in it! If you don't write a feature upgrade event for all your custom features before youdo the upgrade, your feature directories don't get copied over. The majority of errors I have for this health Analyzer Rule is from this very fact. All I had to do was to move the older features over to the new 14 hive features directory. Then all was good!
You can also reference this older post about the other causes of this error here.
Chris