Re: Cannot connect to X server

[Richard Stallman]

    This problem seems to occur when Emacs 21 is called from a very busy
    network link. Although the X authority is correctly set, everything
    occurs as if was not.

I wonder if this is because signals (perhaps to poll for input) are
interrupting some Xlib call.  Can you try finding the Xlib call which
Emacs is in during this time?  Maybe with GDB you can find out if some
kind of signal is in fact happening during that call.

If it is SIGALRM, for an asynchronous timer, try inserting calls to
stop_polling and start_polling around it, and see if that helps.