How to find errors in my mod?

[Mad_Max]

Did some testing the last days.

Start-pos file works; testing till 1120. Restarted the game with my heroes, also working.

edit: restarted the game with some minor changes to original unit-file (prerequisites, availability...): no problems

At 1125 I added a selfmade cav, produced some new units, also working.

At 1130 I added naphta-catapults from an other mod. built a unit and moved the to the front, working. At 1134 the game crashed, when clicking on a certain province. After some tests the save game dindnt load anymore. crash during loading screen.

Any hints?

Max