Sorry, but I've never had this problem, although I can think of numerous times that I should have.

I take it you can't do a repair by running the installer again and using a "repair" option?

In my Window 7 Control Panel\Programs and features, when I right click on PXXG_MD11_FSX, I get the option to Uninstall or Change, when I select Change, I get he installer window (don't know what else to call it) open with 3 options - Modify, Repair, and Remove. Try the repair from that.