Uninstall Avisynth+ - it should revert back previous Avisynth 2.6 installation.
Avisynth 2.6 - https://www.videohelp.com/software/Avisynth
After installation replace avisynth.dll with that MT build: https://forum.doom9.org/showthread.php?t=148782
Besides if your OS is broken that hard you probably should think of clean installation...