Eratosphericals password has been emailed to all active members who qualify for access, so check the inbox associated with your Eratosphere profile email. After you're logged in to the Sphere, you need to use that password/access key as an additional step to get into that forum or the sub-forums.
If you didn't get it and feel you should have, PM me.
P.S. - This is a good time to make sure your profile email address is still valid, else Eratosphere notices such as the one described above won't make it to you! To verify or update your email address go here.