I've taken all the steps to setup a multi site, edited

Hi, I've taken all the steps to setup a multi site, edited wp-config, ht access etc and the dashboard shows the network setup...my issue is when trying to access the network dashboard I get this error
Fatal error: Call to undefined function get_current_screen() in /home/str0ng/public_html/wp-admin/network/settings.php on line 22
Can you advise how I rectify? I've tried to install the network a couple of times to no avail.