Thanks so much for a great plugin. One question:
I see at line 142 of co-authors-plus.php, you seem to be registering a taxonomy named "author". Granted, there seems to be an abstraction layer there, as the name of the taxonomy is just "$this->coauthor_taxonomy" on line 164.
I have had problems in the past with author archive 404's when there is a taxonomy called "author" elsewhere in the theme.
I think a similar conflict is happening because of your otherwise excellent plugin, although obviously I'm not able to connect all the dots.
Bottom line: When your plugin is not active, our /author-sitemap.xml validates just fine as per google webmaster tools. When your plugin is active, it fails with this error message at line 4:
We were unable to read your Sitemap. It may contain an entry we are unable to recognize. Please validate your Sitemap before resubmitting.
The first 4 lines are:
<?xml version="1.0" encoding="UTF-8"?><?xml-stylesheet type="text/xsl" href="http://www.lifelinelaw.com/wp-content/plugins/wordpress-seo/css/xml-sitemap-xsl.php"?> <urlset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd" xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"> <url>
Any thoughts? To further complicate matter, this sitemap is generated by the Yoast SEO plugin.