Instead of change permission to 666, better to change owner of php5-fpm.sock and set permission to 660.
Go to /etc/php5/fpm/pool.d Open www.conf (sudo nano www.conf) Uncomment all permission lines, like:
listen.owner = www-data listen.group = www-data listen.mode = 0660 Restart fpm (sudo service php5-fpm restart)