Hi again.
I have found a solution that seams to work for the moment. It is however more a hack than anything else.
1) Open the file template-1.html you can find in the template folder of the plugin.
2) View the source code and copy it to the clipboard.
3) Go to the settings page of WP Better Emails.
4) Click on the little “html” at the editor window.
5) Paste the code in the editor and press the little x in the top right (e.g. go back to normal view) You should now see most of the template.
6) Replace those part of the text that should not be static (e.g. %content%, %blog_title%, …)
7) Save and test (I had to save it more than once. There was an error on the first attempt.
After this the plugin was working for me. Hope this helps.