In the "Seasons" folder there is a "Light_Winter" sub-folder has a "BNCLOUD0.TER" file in it. This file causes a CTD when the "seasons" folder is in use and the month is set to November.
As this may happen rarely the fault seemed to be intermittent.
The fix is easy
Go to the "Light_Winter" sub-folder and delete the "BNCLOUD0.TER" file.
The default one will be used, but it seems to be OK
I will investigate further. The original files were one of Paul Wilson's terrain sets.
Jel