The coins had 6 confirmations already. So i think its the server itself that wanted a fee. Because instantly after i changed the server no errormessage appeared anymore. Possible?

When this would be a security against some kind of ddos then it doesnt look like a far advanced one. I mean someone who wants to do this surely can change a line of code in an open source wallet to prevent the fee if its included in the client. Or if its the network itself then simply create a script that creates new addresses on the fly and sending back and forth the money to a new address everytime. Would take more processortime but would solve the feeproblem. But maybe this was taken in advance already.