Quite easy to reproduce:
Go to
http://mail.wikipedia.org/mailman/htdig/wikien-l
Click on any item in the "downloadable version" column, say the one
for december 2006.
It's a link to
http://mail.wikipedia.org/mailman/htdig/2006-December.txt
And htdig (?) then tells you "No such list 2006-december.txt".
However, it should probably link to
http://mail.wikimedia.org/pipermail/wikien-l/2006-December.txt
as does
http://mail.wikimedia.org/pipermail/wikien-l/
(to anticipate a response: Yes, I guess the very first link might not
really be a good start page to browse the archive, yes, you should
rather use the second one with the pipermail in it, yes, only the
second one is linked.
But still, as it delivers intelligible output, the links should be correct).
Michael