Date: 4 Jun 1997 00:00:01 EST

  First, make sure your DISPLAY variable is syntactically correct.  For
  example, to display applications on a machine named "enterprise",
  whose IP address is 123.45.678.90, DISPLAY should be set to
  "enterprise:0" or "123.45.678.90:0". 

  Next, try to "ping" the machine to which your DISPLAY variable is
  set.  If this does not work, you have either specified an invalid
  hostname, the host is down, or you are having network problems.
  If you are running an older binary that expects to see /etc/resolv.conf
  in /usr/etc, you will either have to make a symbolic link from
  /usr/etc/resolv.conf to /etc/resolv.conf, or set the DISPLAY variable
  with a numeric address.

  If you see messages like "permission denied" or "can't connect to
  server", you have a permission problem.   Do 'xhost +yourmachine' on
  the remote machine to give 'yourmachine' access to the remote
  machine's display. (Note that 'xhost' is inactive by default on
  SGIs.)

  If you're using NIS (YP), make sure the client is linked with
  "-lsun".

  For more information see Chapter 3 of the X Window System User's
  Guide.