That error is an issue within the Chassis file for the T-90A. It has nothing to do with any other installed skins. (With the way the game works the tanks script file references completely different files for Milky's T-90A than it does for any other skin that is installed.)
I'll forward this to Milky to see if theres any issue with the T-90A in particular. I dont use the skin, so I dont have the files, otherwise I could check and see what is wrong.