Re: "Error Windows Cannot Find '"C:\Program Files (x86)\SEGA\Medieval II Total War\mods\Third_Age_3\Third Age.bat'"
Hmm, very odd.
Did you already clear the virtual store of any TATW related files as Elvenkind suggested? Have you restarted you PC during any of the install process? (You need to restart to actually disable UAC)
You mention you did a fresh install. So, you have previously had TATW and M2TW installed before? Perhaps something got corrupted in the registry. Run a registry cleaner like CCleaner.