Try uninstalling the game, and then run Karens Registry Pruner against the system to remove orphan registry entries for the flight simulator. Also go to program files and remove the folder if it is still there after these 2 procedures to be sure that the install is clean before attempted again.
Some programs have bad / dirty uninstallers that leave remains behind after removal and manual procedures need to be run to clean up the mess.
http://www.karenware.com/powertools/ptpruner.aspWhen adding extra features to a game sometimes there are also other files associated with the added feature/object, such as DLL files etc. Missing these can cause the game to puke when it expects a handler that is missing when launching the program.
