Hey,
You don’t have to answer anymore! The trick was really simpel. One: Firefox responded all of a sudden, so I could delete subscribers (that didn’t work either) and the subscribers I wanted to edit had subribed two times. One time with a wrong e-mailadres and the second time with the right emailadres. If I wanted to change the wrong to the right one, there would be two subscribers exactly the same. That is impossible and that is the reason it didn’t save the changes.
Have a really nice day!
For my fellow users who also have this problem. try these options one by one:
1. Try different browser
2. Deactivate your other plugins. If this does the trick. Activate them one by one to find out which one causes the problem.
3. Try another template
4. See what happens when you subscribe someone in the frontend of your site. (that’s when I got the message that they were already subscribed.)
