Long time user of the model but never saved the flightplans into the FMC.  Just never had a problem entering flight plans quickly.

However, I started to save some into the FMC.  Some of them load just fine but more often than not, selecting a flight plan to load will cause the whole program to crash.

I've done a thread topic search but I can't find any that discuss this issue.  Any ideas on the problem?

Are you saving the flight plans using the CDU (.rt format)? Or saving them in the .PLN format using the default FSX Flight Planner, or a third party flight planner?

I don't save the flight plan (.rt format) with the SID and STAR included. While the SID is normally fine, I always have to redo the STAR so that the landing RWY is added to the flight plan, and the ILS Freq/Hdg is included in the NAV RAD page of the CDU.

Edit. If you have the Captain Sim 777, the .rt files are not compatible with the Captain Sim 757 & 767 CDU, which might be the cause of your 757 crashing when loading a plan.