Yum Update IOError

I run yum every night using cron.  It's worked for years with my current
configuration, but last night I received an error:

==============================================
/etc/cron.daily/yum.cron:

Error getting file http://install.linux.duke.edu/pub/linux/updates/centos-3/i386//headers/kernel-source-0-2.4.21-52.EL.i386.hdr
[Errno 4] IOError: HTTP Error 404: Not Found
Error getting file http://install.linux.duke.edu/pub/linux/updates/centos-3/i386//headers/kernel-source-0-2.4.21-52.EL.i386.hdr
[Errno 4] IOError: HTTP Error 404: Not Found
==============================================

Here's my yum.conf file:

==============================================
[main]
cachedir=/data/cache/yum
debuglevel=2
logfile=/var/log/yum.log
pkgpolicy=newest
distroverpkg=redhat-release
tolerant=1
exactarch=1
retries=20

[duke-base]
name=Linux@DUKE Centos
$releasever - $basearch -
Base
baseurl=http://install.linux.duke.edu/pub/linux/base/centos-$releasever/$basearch/
gpgcheck=1

[updates]
name=Linux@DUKE Centos
$releasever - $basearch -
Updates
baseurl=http://install.linux.duke.edu/pub/linux/updates/centos-$releasever/$basearch/
gpgcheck=1

[duke-distrib]
name=Linux@DUKE Freely
Distributable add-on
packages for Centos
$releasever - $basearch
baseurl=http://install.linux.duke.edu/pub/linux/add-on/distrib/centos-$releasever/$basearch/
gpgcheck=1

[duke-nondistrib]
name=Linux@DUKE
Nondistributable add-on
packages for Centos
$releasever - $basearch
baseurl=http://install.linux.duke.edu/pub/linux/add-on/duke/centos-$releasever/$basearch/
gpgcheck=1
==============================================

I cleaned all the headers using yum clean headers and then ran yum update:

==============================================
[root@fondue ~]# yum clean headers
Gathering header information file(s) from server(s)
Server: Linux@DUKE Centos 3 - i386 - Base
Server: Linux@DUKE Freely Distributable add-on packages for Centos 3 -
i386
Server: Linux@DUKE Nondistributable add-on packages for Centos 3 - i386
Server: Linux@DUKE Centos 3 - i386 - Updates
Finding updated packages
Cleaning all headers
[root@fondue ~]# yum update
Gathering header information file(s) from server(s)
Server: Linux@DUKE Centos 3 - i386 - Base
Server: Linux@DUKE Freely Distributable add-on packages for Centos 3 -
i386
Server: Linux@DUKE Nondistributable add-on packages for Centos 3 - i386
Server: Linux@DUKE Centos 3 - i386 - Updates
Finding updated packages
Downloading needed headers
openoffice.org-0-1.1.2-40 100% |=========================|  99 kB    00:00
cyrus-sasl-0-2.1.15-15.i3 100% |=========================| 6.8 kB    00:00
cyrus-sasl-plain-0-2.1.15 100% |=========================| 4.7 kB    00:00
tzdata-0-2007h-1.el3.noar 100% |=========================|  32 kB    00:00
qt-1-3.1.2-17.RHEL3.i386. 100% |=========================| 9.8 kB    00:00
retrygrab() failed for:

http://install.linux.duke.edu/pub/linux/updates/centos-3/i386/headers/kernel-source-0-2.4.21-52.EL
.i386.hdr
  Executing failover method
failover: out of servers to try
Error getting file
http://install.linux.duke.edu/pub/linux/updates/centos-3/i386/headers/kernel-sour
ce-0-2.4.21-52.EL.i386.hdr
[Errno 4] IOError: HTTP Error 404: Not Found
======================================================

So, yum is able to get some updates, but not others.  I looked around a
bit more and found the reference to the kernel-source in my
updates/header.info file so assumably that's why it's looking for that
particular file.  And it seems that the kernel-source file is not on the
web site.  So, there seems to be a disconnect between the header file and
the repository but I don't understand how it happened or what needs to be
done to fix it.  Any ideas would be welcomed.