Hi there and welcome to TWC forums! 
This sounds like a wrong installation, have you disabled UAC before installing TATW?
If you didn`t do it before installing TATW, go here and apply step 3 from section How to fix it for your main M2TW folder ( even if you have M2TW steam version)
After that, if you have steam M2TW version, reinstall TATW using one of these three methods here.
If you don`t have M2TW steam version, then do the following:
1, Uninstall TATW using Control Panel\ Uninstall program.
2. Delete manually Third_Age_3 folder in your C:\Program Files (x86)\SEGA\Medieval II Total War\mods folder.
3. Unhide hidden folders:
On your DESKTOP, click on START in the bottom left corner, in Search Programs and Files type in Folder Options, click on Folder Options, go to VIEW section, and in Hidden files and folders check the box next to SHOW hidden files, folders or drives. Apply, and OK.
4. BEFORE installing Third Age again, go to Virtual store ( C:\ Users\ [user name or your PC`s name]\ AppData\ Local\ VirtualStore\ Program Files (x86)\ Medieval 2 Total War\ mods folder), delete Third_Age_3 folder found there.
5. Install all four TATW parts - TATW part 1 and part 2, TATW patch 3.1 and TATW patch 3.2 ( CHECK the INSTALLATION paths carefully for ALL Installers, in your case it is C:\Program Files (x86)\Games\Medieval II Total War).
Hope this helps.. Good luck!