I found this reference to a similar error message at
https://bugs.launchpad.net/ubuntu/+source/apache2/+bug/651134
and also
https://lists.ubuntu.com/archives/ubuntu-server-bugs/2011-July/059120.html
via google.
I didn't drill down to see how/if the bug was resolved. You may need
to post this question on an ubuntu list. They may be familiar with this error message.
Hope this helps.
-- Mike