Cause

This message is immediately followed by the "Xlib: Client is not authorized to connect to Server" message. These messages indicate that an X windows application tried to run on the X server specified inside double quotes, which did not allow the request. The "0.0" represents the display device, which is usually the console. If no server name appears, the superuser probably tried to run an X application on the current machine in an X session that was owned by somebody else.