“You cannot access the private section of this site.”
I checked the global config permissions, everything seems fine. I am not sure what am I missing.
The only way for a user to login, is to have super user permission, or to login through social (facebook,twitter,google).
I've checked that nothing on the pages are set to anything other than public access, from articles, article categories to menus plugins.
I've also tried disabling all non-standard joomla plugins, components, modules etc.
After setting up a test-environment, I've tried to delete all users and creating a test user, which didn't help either.
Thought that it might could be a problem with the login module (Improved Ajax Login & Register), so i tried with the standard joomla login module, still same problem.
After all that i tried changing template, overwriting plugins, libraries etc., to correct any errors or problems in the joomla core files - still no luck.

Right now i'm in the need of some professional help, figuring this error out.