I just had a strange and extremely misleading error message in Google Webmaster tools relating to a sitemap file. We normally only submit one sitemap per site as the sites we develop tend to be quite small. One of the sites we have been working on is however much larger and the sitemap file was huge so I chose to split it into several files on the following paths:
When I submitted the website to webmaster tools I was getting the error message "Paths don't match. We've detected that you submitted your Sitemap using a URL path that doesn't include the www prefix (for instance, http://example.com/sitemap.xml). However, the URLs listed inside your Sitemap do use the www prefix (for instance, http://www.example.com/myfile.htm)" as shown below:
This was a bit of a suprise considering that the sitemap was submitted from the same domain as the site and the error message seemed to be telling me otherwise.
After a bit of searching round I found out that sitemap files must reside in a directory which is the parent of the files referred to in the sitemap. So moving all of my sitemap files to the root eventually fixed this issue.