I upgraded from Crossover 13.2 on Linux to Crossover 14.0 and Medieval II Total War Kingdoms now fails to run (using Steam which seems to work OK). It fails with an "unknown error".
This occurs in both Ubuntu 12.04 and 14.04.
I re-installed Crossover 13.2 and it started working again.
I don't have another game to try under Steam, so I'm not sure if it affects other Steam games.