We're currently having a problem with the Group Invites page which isn't allowing you to actually accept an invitation to join a group. I've got a ticket in to get this fixed as soon as possible. In the meantime, I apologize for the inconvenience.

This will not affect anyone creating their own groups or joining groups, unless it's the group owner/moderator sending invitations out. So feel free to continue playing on the site! I'll let you know when we've got this fixed.