Registered users can't login to joomla frontend but Administrator can login with no issue but registered users just can't and the get the warning "You cannot access the private section of this site"
In Joomla 2.5 (and all releases since 1.6) there is a table #__assets that is largely invisible to users, but if the assets have improper values this can cause serious problems for your site, it could happens for a joomla update etc...
The fix is really simple just add this code to your database (replace # that with your db prefix (j17_))
UPDATE `#_assets` SET `parent_id`=1 WHERE `parent_id` = '0';
UPDATE `#_assets` SET `parent_id`=0 WHERE `title` = 'Root Asset';