I have run into this problem a couple of times. The fix or the problem I had was the pilot logbook was corrupted as fsx uses this to reference to on start up. I found a logbook editor that allowed me to edit my existing logbook without losing what I have flown in hours and such. Here is the link: http://lc0277.gratisim.fr/software.html
Try that. Or just delete your logbook in you FSX Simulator Files folder in your Documents folder.
Good luck!
Joe Smelser