To add to the post above:
If you are at the point where all else have failed, and you are about to re-install, try this one last thing.
If you navigate to the location your main FSX folder, (NOT c/program files/microsoft games/microsoft flight simulator x, but c/program files/microsoft games/) and right click on the FSX main folder, and select "properties", a dialog window will come up, with several tabs at the top.
One of those tabs saying "Previous Versions", it will list versions of your FSX folder that System Restore saved. Select the time *before* you updated or did whatever you did that "caused" the error, and open it, and copy the contents into your current fsx installation.
In reality, what you are doing is a system restore of your FSX folder.