C program files Sega Medieval 2 total war. In the Mods folder under Third Age Total War theres 3 folders (data, packs, preferences) and 4 files (icon, config, unit stats excel sheet, and a batch file). I am currently re running both installers to see if that will fix it.
You have Kingdoms installed, right? The same problem can also occur if you have a cracked game but if that's the case we can't help you here.