When I was having a problem with the program crashing when trying to run a scenario, Peter suggested this:
"One thing to try if the scenario database is possibly corrupted, Close TS2015/STEAM, navigate to DRIVE:\Folder\STEAM\steamapps\common\railworks\Content and rename the SDBcache.bin file and the SDBCache.bin.MD5
Reboot
Open Steam/TS2015 and a new scenario database will be built (takes time especially on a slower machine)
If the scenario db was corrupt that should fix it (Ref Gary gptech on UKTS)."
You could give it a try.