@ Carlpea and all the others with this problem
Today i contacted D-Link Support here in Germany.
They seemed very suprised about our difficulties with the Print-Server built in the DNS-320.
But they asked me for my configuration-backup including all the users and their passes, they will try to reproduce the failure..

sounds good so far...
so, if there are any sensational news i will let you all know...
in the meantime: Let's have a cup of coffee.... (or some beer, cause at least i'm a bavarian)

p.s. sorry bout my english, it's a long time ago i visited school...