Apparently it's because the game is trying to load in player-saved army presets. You'll either have to manually delete them in X:\Users\XXXXX\AppData\Roaming\The Creative Assembly\Attila\army_setups or launch them game in vanilla and delete them in game before restarting the game with mods enabled.

That worked for me.

I have the same problem can you please help me ? i am trying to locate what so callde as vanilla but i cant and the games i have downloaded throygh steam. Please help me