Yum troubles

I did as suggested: deleted the first line of yun.conf with vi and inserted [main] instead, but nothing changed.

after <yum check-update> the following message appears:

[peter@localhost peter]$ yum check-update
Gathering header information file(s) from server(s)
Server: Fedora Core 2 - i386 - Base
Server: Dag RPM Repository for Fedora Core
Error - /var/cache/yum/dag/header.info cannot be found
Please ask your sysadmin to update the headers on this system.

In vi my yum.conf looks like this:

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


[base]
name=Fedora Core $releasever - $basearch - Base
baseurl=http://download.fedora.redhat.com/pub/fedora/linux/core/$releasever/$basearch/os/


[updates-released]
name=Fedora Core $releasever - $basearch - Released Updates
baseurl=http://download.fedora.redhat.com/pub/fedora/linux/core/updates/$releasever/$basearch/


#[updates-testing]
#name=Fedora Core $releasever - $basearch - Unreleased Updates
#baseurl=http://download.fedora.redhat.com/pub/fedora/linux/core/updates/testing/$releasever/$basearch/


#[development]
#name=Fedora Core $releasever - Development Tree
#baseurl=http://download.fedora.redhat.com/pub/fedora/linux/core/development/$basearch/


[freshrpms]
name=Fedora Linux $releasever - $basearch - freshrpms
baseurl=http://ayo.freshrpms.net/fedora/linux/$releasever/$basearch/freshrpms/
gpgcheck=1

[dag]
name=Dag RPM Repository for Fedora Core
baseurl=http://apt.sw.be/fedora/$releasever/en/$basearch/dag/
gpgcheck=1

Looks like one problem is solved (sorry if I am a little bit slow in getting the message), but a problem with missing headers seems to be still there.
Please has anyone a suggestion? How does one update headers on a system?
Peter.