Users unable to register - receive super admin..

I was wondering why I was not getting any new user registrations until a person emailed to say that she could NOT log in at all. She is receiving a 'Message from webpage' that 'Only users with Super Admin permissions can change other Super Admin user accounts.'

I quickly tried this in both IE and FF and received the same message in both browsers when trying to register as a new user via the CB Login process.

What could possibly cause this? Its probably been like this for over a month so I have no idea what could have changed to cause this issue.

Any suggestion on what to check would be greatly appreciated.

Joomla version?
CB Version?
CBSubs version?

Exact steps to replicate?

Sounds like you made some plugin or tab available only to superadmin group.
Suggest you keep everything public if you are not sure.

I'm using CB 1.8 and Joomla 1.7.3

I did notice that the CB user Manager > Users Configuration was set as follows:

Allow user registration = yes
New user Registration Group = --Administrator
Guest User Group = Public
New user Account Activation = Admin
Frontend user Parameters = show
Frontend Language = show

I tried changing new user registration Group to 'Registered' and I was then able to log in and permissions seem to be working again.

My problem is that it was working fine for 6 months and then something changed (unable to determine what) so unable to determine what could have caused this to change. But it appears to now work correctly again.

IAAF wrote: I'm using CB 1.8 and Joomla 1.7.3

I did notice that the CB user Manager > Users Configuration was set as follows:

Allow user registration = yes
New user Registration Group = --Administrator
Guest User Group = Public
New user Account Activation = Admin
Frontend user Parameters = show
Frontend Language = show

I tried changing new user registration Group to 'Registered' and I was then able to log in and permissions seem to be working again.

My problem is that it was working fine for 6 months and then something changed (unable to determine what) so unable to determine what could have caused this to change. But it appears to now work correctly again.

Well those settings are NOT CB settings. They are Joomla settings.
The CB Installation guide tells you to disable Joomla registration process - looks like you didn't.

Anyone registering (via Joomla or CB) will become an Administrator.

I don;t think you want this.