I just validated the sitemap generated by the latest version of AutoSitemap, and am being told it is invalid. I used this free service:
https://www.inspyder.com/free/SitemapValidator.aspx
I am being told:
The element 'url' has invalid child element 'lastmod'. List of possible elements expected: any element in namespace 'http://www.google.com/schemas/sitemap-image/1.1, http://www.google.com/schemas/sitemap-mobile/1.0, http://www.google.com/schemas/sitemap-video/1.1'.
Is this related to this: https://webmasters.stackexchange.com/questions/50440/why-is-this-date-in-my-sitemap-invalid-according-to-google ??