Yeah, FOSSIL and JoiPlay don't get along very well.
If you're able to get into the game files to rename things, there's an alternate index file called fossilindex. Try renaming "index.html" to "indexoriginal.html" and that "fossilindex.html" file to "index.html." If that doesn't fix it, there should also be a "FOSSIL.js" file in another folder - make sure that is in all-caps, or the file may not be getting read properly. For example, "Fossil.js" and "fossil.js" are wrong, and might be causing the error.