XEmacs suddenly doesn't work on my Mac

Lynn David Newton writes:

 > I'm running XEmacs beta (21.4 patch 22) on my up-to-date iMac running
 > El Capitan. (Mac OS X 10.11.5)

I'm running XEmacs 21.5.recent, same version of Mac OS X on a MacBook
Pro.  XQuartz is XQuartz 1.18.99.1 (xorg-server 1.18.99.1) (you can
copy-paste that from the X11 menu, About).  I'm running the MacPorts
version.  I may try installing the current versions of XQuartz from
xquartz.org next week, but I too have work to do....

 > After installing the new version, when I start XEmacs the usual way
 > (from a menu ... but I also tried it from a terminal command line), I
 > get this message on STDERR:

By "terminal", do you mean an X terminal such as xterm, or do you mean
Terminal.app?

 > X server not responding
 > : "/private/tmp/com.apple.launchd.zC9wJRhG9U/org.macosforge.xquartz:0.0"

Neither Google nor the XQuartz tracker are helpful. :-(  Just
guessing, but ...

Did you restart X?  There could be a library mismatch such that the
new library is looking for X in all the wrong places.  You could also
try rebooting (I know, it feels like Windows "a good reboot solves
most problems", but you're desperate, right?)

Perhaps you have multiple installations of X and XEmacs is linked to
the wrong libraries (which just happened to work before).

There is a really stupid bug in Mac OS X such that named socket names
have a really short length limit.  Yes, it's so short that it's
conceivable that the above is too long.  This bug bit TRAMP a while
back.  TRAMP is written in LISP so I hacked around it, then Michael A
fixed it upstream pretty quick.  X is another matter....

Are other X apps working?

Where did you get XQuartz, and in what form?

 > I've considered biting the bullet and switching over to GNU Emacs, but
 > I really, really don't want to do that. I *like* XEmacs the way it is,
 > and just want it to continue working for me. Besides which, I'm buried
 > in work and don't really have the time.

You can get an older version of XQuartz at
https://www.xquartz.org/releases/index.html.

You could also try the MacPorts or Homebrew versions (if you have one
of those distros installed already, but I wouldn't recommend 

Good luck!

Steve