I have the exact same issue – the only way I can remove the errors is to set wp-config.php to 777.
The recomended 755 produces the following errors –
Error: Could NOT enable Quick Cache. Please check permissions on /wp-config.php, /wp-content/ and /wp-content/cache/. 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.
It IS set to 755…