Dashboard problem when users sign

Whenever anyone signs up to create a site, they automatically get this message when they login;
You attempted to access the "Main Site" dashboard, but you do not currently have privileges on this site. If you believe you should be able to access the "Main Site" dashboard, please contact your network administrator.

If you reached this screen by accident and meant to visit one of your own sites, here are some shortcuts to help you find your way.

Your Sites
New User Site Visit Dashboard | View Site

How do I fix this?