Specific user role can't log in I'm having a very strange problem: 
Most user roles can login without a problem (administrators, clients, etc...).

But users with the 'registered user' role can not login through the form. The login form does not respond. In the log messages the failed login attempts are not logged.

The only way the users (with role 'registered user') can login is through the request new password link.
So the user clicks on the link, receives an email with a login link, and when they click on the link in the email they are logged in. So than they can edit their account and even change the password.

However, when they log out again and try to login with the new password it does not work anymore, the form does not respond again. 

The only way that user can get logged in again is through the request new password procedure.

Anyone have any idea what could be causing this?

I suspect it has something to do with some kind of permissions.
Some of the modules i installed who could maybe give a conflict:
Logintoboggan, Registration role

Any help would be greatly appreciated.

Greetings
Thanks for the help.

I did try to login with an email and username, same results for both.

But very strangely everything works now...
And i have no idea what i did to fix it.

Last thing i did was update every module and the Drupal Core.
And today the login form works again as it should...

I would love to give more information for future people experiencing this problem but frankly i have no clue what solved it.

Thanks again for all the help!

Greetings