Samba-share access only by servername, not by ip


I encounter a strange behaviour like described in this post.
Entering a samba-share from a win7-client by\\10.0.0.x\sharename\ leads to the following error-message, but \\servername\sharename\ works well.


The firewall-entries are set like in the above post but the problem occurs all the same.
Surprisingly it came up over night, without any changes having been made to the system nor to the clients, no windows updates etc.
DNS seems to be ok, ping and nslookup works, the umc can be opened by typing the IP.
Stopping the firewall doesn’t change the situation.
A problem with udn replication exists since 10 days but the prob here is ‘brandnew’ , so I don’t assume them to be related.

Does anyone have an idea?