I am NOT telling you to 'upgrade' Moodle. You have installed a version of the Binarus theme that is for a NEWER version of Moodle than you are running. You need to:
- Go to your 'themes' folder and delete the 'binarus' folder.
- Replace with the one attached (after unzipping). Which is the 'Binarus' theme from Moodle 2.5.6+ (Build: 20140522) - which should be compatible with your 2.5.6.
- Go to 'Site Administration' -> 'Notifications' and click on 'Upgrade Moodle database now'. This will NOT upgrade Moodle to a higher version but instead install the plugins correctly.