[nerbert]

Try putting this line just above the $templater->register one

$templater = vB_Template::create('SHOWTHREAD');

I'm not very good at this stuff but just keep in mind that as long as you have all your stuff inside that conditional in the plugin you are the only one who will get errors.

EDIT: That's not my plugin but that error is from mine. I don't know why you get an error and I don't.