Need Help Configuring User Registration with Invite & ProSites

I want to be able to add users to sites by invite only (from the super admin or site admin). I'm having some trouble when the Invite link goes to the ?=register URL. It tries to load my prosites pricing table and the whole process ends there.

I will eventually open my network up as a full DIY solution, but for now, I just want a better (but still fully managed) user registration procedure.