ob_start(): second array member is not a valid method

I installed a web application, but while opening the web application in a browser getting message

Warning: ob_start(): second array member is not a valid method in /opt/lampp/htdocs/-/mainfile.php on line 80

Notice: ob_start(): failed to create buffer in /opt/lampp/htdocs/-/mainfile.php on line 80

I saw the mainfile.php, the statement throwing this message is :

ob_start(array('ob_gzhandler',5));

ob_start('ob_gzhandler') is working fine but if array() is used its not working.