Steam issue

Hi,

I have installed Arthur Total War on the steam version, following the instructions given. However, when I attempt to play a custom map or the campaign, I am simply redirected to the menu. When I try to play a historical battle, the game crashes. Finally, I decided to play a custom battle on one of the regular BI maps, and it began to load - then the game crashed, and I got this message.

script error in bi/arthur/data/descr_model_battle.txt, at line 426, column 20.

Model database failed to load model arth/data/models_unit/ATW_dinuadda_claiomhnaghta.CAS.

What does this mean, and can I fix it? I never had this problem on the disc version, but thanks to Windows 10 the old disc version simply isn't playable anymore.