Fatal error: get_current_screen, eNewsletter


I've installed the eNewsletter plugin and get this message when creating a newsletter:

Fatal error: Call to undefined function get_current_screen() in /var/sites/s/staging.birdswood.org/public_html/wp-content/plugins/fusion-core/fusion-core.php on line 920

I'm no PHP expert.

Lines 919-921 say:

function fusion_add_quicktags_button() {
if( get_current_screen()->base == 'post' ) {

Could someone please help?

Happy to give Support Staff access but my site is currently on staging and password protected. Can email Support directly if that helps.