there are many factors involved like folder structure, file structure - common files folders/subfolders etc…
that’s why Lesterbangs created a bundle for it, download it… install it in thumbgen and it will work just fine
if you still can only access the non removeable default template from the drop down box you need to wipe thumbgen completely from your hard drive, re-install it with a different name and location if you don’t know how to make a “clean install”
