Problem with rebelling city

[Mad Hoplite]

Most probably it's a slave unit in descr_rebel_factions.txt with no "slave" in export_descr_unit.txt or no texture or model_sprite lines for slave in descr_model_battle.txt.

This is from the A modder's guide to CTDs thread:

In Campaign Mode CTDs:
During play/AI turn:
- A family member being generated without a general_unit for the faction.
- A new character is generated and not given a valid name.
- Some building bonuses in the same building level as certain unit recruitment strings (this will happen both during AI turn and when the building is right-clicked).
- Units able to be recruited in EDB but no faction "ownership" for a faction in EDU.
- Units added to descr_rebel_factions.txt but no slave faction ownership in EDU.
- Units added to descr_mercenaries.txt but no mercenary_unit in EDU.
- Bad defined type of unit for army spawned via script file
- Mismatch between export_desc_character_traits.txt and export_VnVs.txt entries causes CTD when viewing the portrait of a named character with the bad trait.

Hope that helps.