The Transall was programmed for Prepar3d Version 4. With all the recent updates from Prepar3D I have tested it on version 4.1 and it worked fine. Unfortunately, having tested it on Version 4.4 today, something that Prepar3D has done in this new version seems to be causing the Transall to crash.
I am looking into it and will keep you updated on the solution.
Look if you have this dll in the gauges folder - MV_WX.dll . If so just rename it to MV_WX01.dll. Rex weather radar is not compatible with prepar3d v4.4 yet.
Hope it helps.
There is an update for the REX weather radar out since December 20
Changing the dll file will stop other planes that use weather radar from to function correctly.
So how this is still a problem today?