Sorry to hear you are having trouble.

It would help if we could see what's in your debug.err file, it is located in \Documents\My Games\GC3 or \Documents\My Games\GC3Crusade

If you could upload it to a cloud service (DropBox, Google Drive, One Drive) and post a link here, the developers can take a look at it.

Also is this when loading a savegame or for a new game? If it's for a savegame please upload that as well.

Thank you for your patience and patronage.

Not sure whether this is related: I noticed that when I try to start a new game with a large map while another application is using most of my RAM, the game will simply ignore my efforts and jump back to the main menu when I press [start]. No error message, but no crash either. It seemed odd at the time because I hadn't realized I was so low on RAM.

I think I've fixed it using a post from another thread here:

My guess that it is either not downloading all the files that you need from Intrigue or one or more of the data binaries didn't download correctly. You can force the data binaries to rebuild from the downloaded xml by deleting the RebuildData.ini file from the GC3Crusade folder. If that doesn't work, you're probably missing files regardless of what the verify files find and you may need to try doing a full re-install.

Deleting the RebuildData.ini file fixed it after I reinstalled again and still had a problem - after the new INI file regenerated things are working again....so far.