Google Webmaster Tools is now reporting "too many redirects" within Sitemaps files. A WebmasterWorld thread has reported the warnings back last week. I have finally hunted down a screen shot of such an error:
The only way to see this error is to submit a Sitemap file to Google and for one or more of those URLs to contain a redirect of some sort.
The additional help Google links to is over here, which says "When we processed your Sitemap, we found that some URLs aren't accessible to Googlebot because they contain too many redirects. Please change the URLs in your Sitemap that redirect and replace them with the destination URL (the redirect target)."
The specific error I see is a "HTTP Error: 301 (Moved permanently)." But that is the type of 301 redirect Google says to use when "permanently redirecting from one page to another." In any event, it is best to replace the Sitemap file with a file that has no redirects at all.
Forum discussion at WebmasterWorld.