If you are running 1.0.13 and the third party user reg is not patched to work with 1.0.13, that could be your problem. AFAIK, Joomla! changed the way that passwords are encrypted in 1.0.13 and most/all third party registration/login systems were broken as a result.
I am running 1.0.13 and the component is juser. The password registration runs fine, this is a confirmation screen to say check your mail etc and you can set it to point at a static content message. It is the stastic content that is causing the issue.
I have trawled joomla.org fourms and have tried all the listed suggestions without success.