I would go to the following thread by Tinwarble, where you can get all the info you need. There is a link to the tutoriaI, but if you cannot t-shoot the issue, just uninstall and then re-install the Thumbgen templates for the theme. That will put you back to where you started when it was working
If you get nowhere with the above It might be helpful if you could list your settings (or take screenshots) for each of the major categories under “options”, such as “General”, Moviesheets" and “Input/Output Naming”, so we can see what you have setup.
EX: “Input / Output Naming” Tab
Thumbnail: $M$N : JPG
Extra Thumbnail: $M\Folder : JPG
etc…
Good luck
-P
