[Plugin: Google XML Sitemaps] Sitemap Error

I don’t know if this helps your instance, but I had this same error. I traced it to me using pages to divert to external URLs (in my case, another site I own) using the “Page Links To” plugin. The problem therefore was that two domains were showing up in my sitemap, but of course Google only wants and authorizes one.

To rectify, I excluded from the sitemap generation options the specific page IDs that were set up as links.

If you click on the “See Sitemap” link in Google Webmaster tools (or download a copy manually) you can see what it’s trying to index. If any domains that are not on the primary domain show up, that could be the problem.

As I said, I’m not sure if this applies to your instance, but perhaps it might provide a place to look.