Emacs - cannot connect to X server

[Matt Muggeridge]

Environment: emacs on Tru64 UNIX V5.1 and Digital OSF1 V4.0, connecting to
my PC X-Server (Xcursion) across a wide-area cable connection.

When attempting to start emacs, I see:

---------------------------------------------------
    Emacs   WAN Result          LAN Result
   -------   -----------------   -----------------
    20.7      always succeeds    always succeeds
    21.1      mostly succeeds     always succeeds
    21.2      rarely succeeds      always succeeds
----------------------------------------------------

When it fails, the message displayed is:

 emacs: Cannot connect to X server xx.xx.xx.xx:0.0.
 Check the DISPLAY environment variable or use `-d'.
 Also use the `xhost' program to verify that it is set to permit
 connections from your machine.

It seems to be independent of the OS, as I see the same result on Tru64 UNIX
V5.1 and Digital OSF1 V4.0.  It also seems to be independent of my PC, as
I've tried it on one running Windows/ME and another running W2K.

All other X-applications I have tried succeed, even when emacs fails
repeatedly.  E.g. I can successfully run "xeyes", "xterm", "xclock",
"emacs-20.7".  This problem is limited to the versions of emacs above.

I do not understand how emacs connects to the X server, but I am suspicious
of timeouts.  Could it be that emacs does not wait long enough to establish
an X-session over a slow link?

Thanks for any feedback.

Matt.