Hi gidgreen, thanks for your help. To prevent email editing I did change qa-page-account.php: After line 221 I added: 'type' => 'static'.
I got this tip here from q2a-forum.
Now I removed this line, uploaded a new avater, and the errors are gone.
Mhh.. so that brings back the other question: How to disable the edit option for usermails?