Dashboard Access

Hi,

When my users sign up for a free blog, once they have activated and then go to wp-admin to login, they are greeted with this error when they try and access the site:

"You attempted to access the "Site Name" dashboard, but you do not currently have privileges on this site. If you believe you should be able to access the "Site Name" 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."

Basically they can't access the dashboard of their own sub domain directly, a way around it is to go to the menu on their home page and click new post, but Dashboard is clearly not working.

Any help anyone?