Symptom: Sometimes FS will hang on startup , select flight or fly now.
Problem: When saving .FLT files, FS is padding extra garbage on the front. This makes the file too large and I am sure FS is destroying some memory when it loads it.
Quick Fix: Suspect every .FLT that is bigger than 10kb. If you don't need the data, just delete the bad .FLT. ie: Previous flight.FLT. If you do want to save the data you must copy the good data out and create another .FLT. Simply deleting the bad lines with Notepad won't work. Notepad will not change the size of the .FLT and the edited copy will cause the failure again.
I have an open problem with MS and will report what I have found NOW. Maybe be can get this bug exterminated.