I am not so sure of the cause as I am also using wp + php apc + w3tc except it is on nginx. The one that I stated was a reading from somewhere. Now that is mentioned, I just found a site that works out as between php apc and w3tc here. It seems to say that there is apc.ini in the w3tc ini folder which need to be modified. Do read and may be try it out?
thank u change from php_mod to php-fcgi work for me but before that i change in I change wp-config.php by add define('FS_METHOD', 'direct'); to change from FTP to Direct Download Best regards
