The code may lead you to believe you have an incompatible template but if you are not trying to use an old template currently that is not the issue. I actually deleted all 3.x style templates to make sure. What the issue is, is old plugins that are not compatible but Vbulletin does not seem to account for this except that you'll see a fatal PHPerror. You should disable all plugins and then enable one by one until you find the one that is causing the issue. &........