So I found my error:
The problem was in the Federation Tab.
In the field “Domain” I actually wrote down my Counterpart
(for example: In RC-Server “rc1.test.home” i wrote down “rc2.test.home”)
You actually have to specify the server on which you are.
(for example: in RC-Server “rc1.test.home” → In Domain you have to specify “rc1.test.home” too)
Well, but now i have the same problem as mentioned in this topic :
: