Elsőre nálam is ugyanez volt a hibaüzenet (debian stable, gcc). Benne van a leírásban: For this simplification to work we need to disable regular cookie based authentication and allow all app on local machine to connect to X server directly. To to that you need to open a terminal and type xhost +local: Later if you want to revert back you could use xhost -local: to force cookie based authentication back.
És valóban, így már működik.