404. That’s an error.
The requested URL /add?feedurl=http://diaweb.usal.es/diaweb/rss/asignaturas/avisos/avisosTablon.xml was not found on this server. That’s all we know.
/add?feedurl=http://diaweb.usal.es/diaweb/rss/asignaturas/avisos/avisosTablon.xml