I'm getting a conflict between the new E-Newsletter Editor and a plugin called Page Security by Contexture.
The error is
Fatal error: Call to undefined function get_current_screen() in /opt/lampp/htdocs/canhc/wp-content/plugins/contexture-page-security/core/CTXPS_App.php on line 62
Email_Newsletter_Builder::construct_builder_head calls the admin_head action without including the Admin Screen API (wp-admin/includes/screen.php).
I believe any other plugin that hooks into admin_head and depends on the Admin Screen API will be similarly broken.
Steps to reproduce:
Install E-Newsletter 2
Install Page Security by Contexture
Try to create a newsletter