How do I fix this?

I'm receiving a message in /var/mail/mark (my first name) that says:

(gnome-clipboard-daemon: 77xx [where xx is variable, I have about 50 of these messages in the mail-box]: Gtk-WARNING **:Cannot Open Display.

This is the message in the mail-box (this is NOT email--it's from the system),:

From mark@localhost.localdomain Sat Apr 15 22:12:38 2006
Return-Path: <mark@localhost.localdomain>
X-Original-To: mark
Delivered-To: mark@localhost.localdomain
Received: by localhost.localdomain (Postfix, from userid 1000)
id 9E5573D6337; Sat, 15 Apr 2006 22:12:37 -0700 (PDT)
From: root@localhost.localdomain (Cron Daemon)
To: mark@localhost.localdomain
Subject: Cron <mark@lexington> gnome-clipboard-daemon
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: <HOME=/home/mark>
X-Cron-Env: <PATH=/usr/bin:/bin>
X-Cron-Env: <LOGNAME=mark>
Message-Id: <20060416051237.9E5573D6337@localhost.localdomain>
Date: Sat, 15 Apr 2006 22:12:37 -0700 (PDT)
Status: O
Content-Length: 71
Lines: 2

Hi Mark,

The above kind of mails can be received in following situations:_


You tried to open some GUI app from console when X is not there.
or
you tried to login from X using another account and in
terminal window (virtual console like Konsole or gnome-terminal ) you tried to open a GUI app after sudoing mark as user.
or
You connected from network using telnet /ssh(ssh without -X and tried to fireup those apps)

That would account for about 50 messages like the above in my mail-box? OK

I guess it isn't serious. I haven't done any of those things that I know. Nobody else uses this computer. I haven't done more than run Update Manager and Synaptic.

The only reason I continue to pursue this is a problem with the modem/kernel/software dropping the line, freezing the modem/software and causing me to re-start to get back on-line.