What you can do is to enable logging, and then check the logfile after it crashes - it should point you in the right direction.

What you need to do is add a few lines to the .cfg file of the mod you're using (or medieval2.preference.cfg if you're running the 'basic' game)

if you add:
Code:
[log]
to = logs/system.log.txt
level = * error
Into the file in question, you should see a 'logs' folder show up, and a system log will dump into that folder when you run the game.

Take a look at the log when it crashes and it should give you the error, generally with the offending file and line number where the code goes bad.