Did you fight the battle on your own? Try to use auto_win to get automatically resolved battles.
Is there a FM engaged on Sweboz side?

If you can't get across it by autoresolve, first fight the battle while not activating the script, activate it afterwards and look if the game crashes in the next few AI turns.
Keep a backup of your 'clean' save!

If nothing works, upload your save and I'll give it a try on my build. In that case, you have to tell me your exe, used mini-mods and other related stuff.

XSamatan