Error loading mount database?

Yesterday I imported the Praetorian Cohort to BI and it worked fine, then I tried importing the Urban Cohort and I got the following error: "Error loading mount database". So I deleted the Urban Cohort and I still got the error, which resulted in me having to reinstall BI to fix it.

This is the second time i've got that error, last time it was after I added Praetorian Cavalry to BI, can anyone explain why this happens?

I'm guessing its looking for the horse. It should be there (the only entry in export_descr_unit is for a heavy horse). Check descr_model_battle.txt to make sure your entries there are correct.

and descr_mount.