Brilliant test idea! You're right. It worked fine with the default template. At least that narrows it down. I will post this on the template board since it's a problem with the template!
This seems to be a fresh problem from a fresh install. I am also having the same problem. Where can I fin the cb.invite plugin to reinstall???? or where can I disable it ?! Very frustrated. Looked all around but no luck. I am using Joomla 1.5.5 with the latest CB.