Mailpoet Form Editor Blank

Hi all, I’ve set up the plugin and its all working fine, only the form editor is showing blank. At first I get to choose a template form etc, but when I click to select or click the button to start with an empty form it loads a blank page. I already shut down all other plugins and themes, but it is still showing a blank page. So it looks like its not because of a plugin/theme conflict. What can I do to solve this issue?

Thanks for your help!

The page I need help with: [log in to see the link]