Well if you use Google Webmaster Tools or Bing Webmaster Tools you may have noticed that every single web site you run is showing an error on the sitemaps and if you, like me, have not logged into those portals in some time you may be horribly shocked to see that it has been months since Google or Bing last ever read your sitemap.
I think this was caused by an update to Yoast at some point in the last 6 months that changed some little setting somewhere causing your sitemaps to be suddenly broken.
To fix it is very simple. From WordPress click on SEO > XML Sitemaps and then scroll to the bottom of the page and click SAVE CHANGES. Then scroll to the top of the page again and right click where it says “You can find your XML sitemap here”, copy the link. Go to Google / Bing Webmaster Tools, delete the sitemap for your site and resubmit it.
Took me a mere 10 minutes to fix this on 15 sites. Hope it helps you.
I reported a while back on another error in YOAST that also broke the sitemaps, that was for an earlier version of YOAST 1.4.10 …. you can read that article here.