I just downloaded the J41 and tried to load it and FSX CTD'd.
I looked for the fix and found varoius approaches. First I will try the most simple and that is to set the default freeflight airplane to the glider. I will keep posting information until the problem is solved.
PMDG suggests to right click FSX icon for admin user, change the default freeflight to the Ultralight at Friday Harbor and save.
Restart FSX. When the flight opens at Friday Harbor select the J41.