Why is the site showing "Protected Content"?

When I (and others) try to access my site we are getting the following message:

Protected Content

The content you are trying to access is only available to members. Sorry.

I have disabled the membership plug in, logged out, visited the site and still get that message.

Why is the site being protected? Is a different plug-in responsible?
I have only created 3 member levels and none of them were active so I can't see why it would be protected.