The first time you try to run a remote X application, it usually does not work. Here are a few common error messages, their probable causes, and solutions to help you on your way.
xterm Xt error: Can't open display:
There is no DISPLAY variable in the environment, and you didn't tell the application with the -display flag either. The application assumes the empty string, but that is syntactically invalid. To solve this, be sure that you set the DISPLAY variable correctly in the environment (with setenv or export depending on your shell).
_X11TransSocketINETConnect: Can't connect: errno = 101 xterm Xt error: Can't open display: love.dial.xs4all.nl:0
Errno 101 is ``Network is unreachable''. The application could not make a network connection to the server. Check that you have the correct DISPLAY set, and that the server machine is reachable from your client (it should be, after all you're probably logged in to the server and telnetting to the client).
_X11TransSocketINETConnect: Can't connect: errno = 111 xterm Xt error: Can't open display: love.dial.xs4all.nl:0
Errno 111 is ``Connection refused''. The server machine you're trying to connect to is reachable, but the indicated server does not exist there. Check that you are using the right host name and the right display number.
Alternatively, it is possible that the X server was configured not to listen to the usual TCP port. To find out if this is the case, see if the X server is started with the -nolisten tcp argument, and if so, remove it.
Xlib: connection to ":0.0" refused by server Xlib: Client is not authorized to connect to Server xterm Xt error: Can't open display: love.dial.xs4all.nl:0.0
The client could make a connection to the server, but the server does not allow the client to use it (not authorized). Make sure that you have transported the correct magic cookie to the client, and that it has not expired (the server uses a new cookie when a new session starts).