JoomlaPlug!

If you like, open a support ticket and send us your site Joomla admin and ftp details to check the issue!

What i would also recommend i maybe try to reupload the Joomla core files through JoomlaCloner, simply put the Joomla core package on the site, open the Joomla.Cloner.php restore screen, select that package and uncheck the "import mysql" option then follow it as a normal restore! After that, you need to manually delete the installation/ directory

Ovidiu