I'm guessing here that you are running Fedora Core 6 and have done something like the following to get the Crash-hat repo on your system...(I'm going through the same problem!)
wget
http://crash.fce.vutbr.cz/crash-hat.repo
then you will have used the resulting file to update the repo list. The file you got with "wget" has the following content:
[crash-hat]
name=Fedora Core $releasever - $basearch - CrashHat
baseurl=http://crash.fce.vutbr.cz/crash-hat/$releasever
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/Petr.Kristof-GPG-KEY
and the problem lies in the second line, which specifies a baseurl which is specific to the release version ($releasever). The problem is that the release version in this case (again I am guessing!) is "6" for Fedora 6, and the crash-hat site doesn't have files for Fedora 6, it goes as far as 5 and stops. (Look at
http://crash.fce.vutbr.cz/crash-hat, you'll see what I mean)
To get yum going again, go into the /etc/yum.repos directory and remove the crash-hat file, and at least yum should work again.
I'm still trying to get a resolution to the overall problem, so if I get a sensible resolution, I'll post it up, but the way I'm approaching this is that if you look deeper into the site, there is an area:
http://crash.fce.vutbr.cz/crash-hat/testing/live/
which has a Fedora 6 area. I'm a bit concerned by the .../testing/live , but when I get a chance I'm going to do some investigation and see if by modifying the file above with this line, I may get it to work.
HTH
Jimbo