The immediate cause of this problem is a corrupt Revit.ini file, which you should be able to address by copying a good version of this file to the following locations:
C:\ProgramData\Autodesk\RVT 201X\UserDataCache
C:\Users\<UserName>\AppData\Roaming\Autodesk\Revit\Autodesk Revit 201X
In most cases, this problem stems from the unwanted secondary installer (Configuring Revit 201X dialog), which inadvertently corrupts the Revit.ini file because the original installation media is no longer available and the repair process cannot complete successfully. Consequently, one way to avoid this problem is to ensure that the original installation media is still available. However, the drawback of this approach is that users need to sit through the repair process each time it pops up.
The better solution is to eliminate the unwanted secondary installer but the drawback is that this requires Revit to be uninstalled and reinstalled. In this scenario, the key is to install the available Revit updates first and then the Revit add-ins/add-ons.
Tony Michniewicz
Revit Software QA Analyst