does my super cache not work any more

Hello there,we now get this message in our settings,why is that,nothing has been wrong before.
Permissions: Please check permissions on /wp-config.php. Quick Cache needs write-access to this file. Permissions need to be 755 or higher.
Permissions: Please check permissions on /wp-config.php. Quick Cache needs write-access to this file. Permissions need to be 755 or higher.