Dave,
I've just reinstalled the cumulative updates, with Microsoft Security Essentials real time scanning turned off, and I still get the error. The default settings are restored but clicking O.K. on the error message box causes PFE to close.
Although PFE is basically working I've noticed a few other issues, which could be due to mistakes on my part, which don't give me a lot of confidence that everything is OK. First I've never heard the pilot request IFR clearance when pressing '0' although the clearance is given and can be acknowledged. Second when reaching the hold I'm told to contact the tower, so I acknowledge that, change to the frequency given, press '0' and hear the pilot ask for taxi clearance again!
Do you want more detail on the other issues now or should we get to the bottom of the error message first?
Andy L