It could be the script that is firing?
Do you edit the 2da appearance file? If you added a new character.
Also is the tga file- the skin of the new character in the override folder?
Did you restart the game after placing the file in?
If you drop certain files in and then use a save where the script or files added in are in the same model as the save? This could cause bugs.
Also is this part of a new .mod file? Or an existing kotor2 module and you are just changing one if the files ?
I need more info since there are to many things that could cause a bug.