It may happen that you try to login to Joomla Admin and you get following error

The following error is displayed.

* JAuthentication::__construct: Could not load authentication libraries.
* Username and password do not match

The error occurs when you inadvertently disable the plugin “Authentication – Joomla” assuming it was for the front-end authentication. This plugin is for the admin authentication and no one would want to disable this.

All you need to do is access the Joomla database through Phpmyadmin, look for “jos_plugins” table and change it’s field ‘published status’ to 1 .

Now you would be able to login without any problems.