Hi there and welcome to TWC Forums!
Please, do not make posts everywhere for the same thing, better to keep it in one place so that there will be no confusion.
Now, answer few questions:
1. What Windows do you have ( or is it MAC, Linux) ?
2. Is your M2TW steam or non steam version?
3. Have you installed all four TATW Installers, and did you check does your TATW work BEFORE installing MOS?
4. What version of MOS Installer are you using, the Full Installer, or the one with more parts?
5. Did you run Cleaner.bat file found in your ../m2tw/mods/Third_Age_3 = folder where MOS is installed)/ ?