As i wanted to start a TelnetAppender with a Port that is already in use, to handle the Error and inform the User that he should choose an other Port, you simply: catch(IOException e) { e.printStackTrace(); } *(TelnetAppender line 76-87)* And i cannot use the Error anymore. I don't know if this was intended but it sure is useless in this form. (Not only the TelnetAppender)