yum: Cannot open/read repomd.xml file

[Timothy Murphy]

Why, oh why am I getting this mysterious message from yum
on one FC-4 machine?
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[root at alfred tim]# yum update
Setting up Update Process
Setting up repositories
http://download.fedora.redhat.com/pub/fedora/linux/core/4/i386/os/repodata/repomd.xml:
[Errno 4] IOError: <urlopen error (2, 'No such file or directory')>
Trying other mirror.
Cannot open/read repomd.xml file for repository: base
failure: repodata/repomd.xml from base: [Errno 256] No more mirrors to try.
Error: failure: repodata/repomd.xml from base: [Errno 256] No more mirrors
to try.
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I've checked that the repomd.xml file does exist;
I can save it in my browser, but wget fails:
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[root at alfred tim]# wget
http://download.fedora.redhat.com/pub/fedora/linux/core/4/i386/os/repodata/repomd.xml
--13:17:09-- 
http://download.fedora.redhat.com/pub/fedora/linux/core/4/i386/os/repodata/repomd.xml
           => `repomd.xml'
Resolving download.fedora.redhat.com... failed: No such file or directory.
----------------------------------

I get the same error if I change the baseurl:
----------------------------------
Setting up Update Process
Setting up repositories
http://ftp.heanet.ie/pub/fedora/linux/core/4/i386/os/repodata/repomd.xml:
[Errno 4] IOError: <urlopen error (2, 'No such file or directory')>
----------------------------------

Again, I can see the file in my browser.

What, please, is the cause of this problem.
And even more important, what can I do about it?

I googled for the error message,
and while I came up with many instances,
none of the suggestions offered seemed relevant in my case.

I have one other AMD-64 machine still running FC-4,
but this has no problem with yum.
I've even tried using the yum.repos.d files from that machine
in the "bad" machine, but this does not help matters.


Any advice or suggestions gratefully received.



-- 
Timothy Murphy  
e-mail (<80k only): tim /at/ birdsnest.maths.tcd.ie
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland