I noticed the archive links on my blogs weren’t working.  I did some web searching and found an article titled Monthly Archive Links Not Working.  The cause was that I read earlier that it was a good idea to turn off data-based archives in the Joost’s WordPress SEO plug-in.   The reason was to minimize the number of duplicate pages that would be indexed by the search engines.  However, that setting disabled the links.  I re-enabled them.