YES - IT WORKS! (with my FRITZBox 7390)

THANK YOU SOOO MUCH, Tomi, MUCHAS GRACIAS - you are my personal N9 hero - and surely the one of many other N9 users, too. Till today I always travelled with my N9 and additionally my 701 only for VPN reasons. From today on the N9 will travel alone.

EDIT: it WORKED the whole afternoon and now I'm getting again (different) error messages - I will try first to sort out possible errors on my server config and if necessary come back here