404. That’s an error.
The requested URL /add?source=atgs&feedurl=http%3A%2F%2Fumfragen.uni-due.de%2F%3Frss%26list%3Dmain%26lang_id%3D1 was not found on this server. That’s all we know.
/add?source=atgs&feedurl=http%3A%2F%2Fumfragen.uni-due.de%2F%3Frss%26list%3Dmain%26lang_id%3D1