E-Newsletter Customizer does not load

Hey there, as mentioned above: I have difficulties with the e-newsletter plugin.

I already deactivated all plugins and tried it with a standard-theme, but I still can’t create any E-Mails.

I already saw that the Error “The theme directory “Disco” does not exist.” was common over a year ago, but neither the version from the post nor the latest version do work.

This is may be somehow important: the problems started when I tried to upload a custom theme.

At first it was visible and usable, but generating a new newsletter gave me that “iLetter” does not exist error

And the problems persist despite having deleted and reinstalled the plugin