Thank you Dave and Kevin for your quick answers.
Dave you are right that everybody has to look first wether causes lie on his own side and not on the other.
So what you correctly proposed as standard procedure is what was discussed and tried out by members of kartonbau.de forum since saturday. We followed the tips Rickstef gave on facebook, tried different browsers, security functions and hardware using different providers. Nothing was successful except for the use of a VPN.
The thing that I am wondering about is that the phenomenon appeared nearly over the hole country by the same time and only for papermodelers. This is an argument for me that there will be no individual solution and the problem is maybe but not necessarily caused by the papermodelers forum or its environment. This is why I mentioned Rickstefs note on facebook where he spoke of access problems after a data base error on friday.
So we will wait and see. If Kevin is right it will disappear within a few days
Best regards
Nils