Joomla 2.5.11 to Joomla 2.5.11 2.5.14 bug Frontend login error: “You cannot access the private section"

This bug you can solve it easily by using phpmyadmin. You have to run 2 query into assets table.

1) UPDATE `prefix_assets` SET `parent_id`=1 WHERE `parent_id`=0 AND id>1

After executing first query, run the following query:

2) UPDATE `prefix_assets` SET `parent_id`=0 WHERE `title` = 'Root Asset'

I hope this can help you