I'm getting 404 errors for all sitemaps on a subdomain install with some sites mapped using Donncha's domain mapping plugin. But the robots.txt files are working fine for all sites. And the sitemap-news.xml file for the main site is redirecting to Feedburner.
I have tried saving/changing the permalink structure several times along with deleting and reinstalling the plugin. I'm running WP ver 3.1-RC4