Thank you all for your answers.
Yesterday evening i tried some codes again. The seller wrote me some possible numbers. And now, thats strange: I tried '12345' again and my N810 accept it. Why? Why it don't accept yesterday morning? I don't understand. I tried in the morning '12345' more than one time.

@endsormeans, can you tell me more about CSSU on N810? Is this the same like on N900? What i have to do?