Get ready for more acccurate and informative error messages for your Sitemaps. Because Google has enhanced the infrastructure that processes Sitemaps. The one conspicuous change would be more detailed error messages. As new detailed error messages have been added, you will have to click and explore everytime you see an error message that you have not seen before.
This is because we've enhanced our reporting to provide error information that wasn't available to you before. For instance, if you see an "Invalid file format" error, make sure that you've declared the namespace in your Sitemap file correctly and that the header matches the examples we provide in our documentation.
As part of this change, you can no longer list Sitemap index files within Sitemap index files. Each Sitemap index file can list only Sitemaps. Remember that you can list up to 1,000 Sitemaps in each Sitemap index file. If you have more than 1,000 Sitemaps for a site, you can submit multiple Sitemap index files.
If you request verification for a non-existing file , make sure that your server returns a status of 400. This ensures that you are getting the right message and there is no configuration problem with the server. You might also have encountered the message "We couldn't find your verification file. Make sure it is named correctly and is uploaded to the correct location," for files that really do exist. Google has worked upon it so that the right error message is displayed.
If you request verification and we receive a status other than 200 or 404 when we try to access a non-existent file on your site, you'll now see an "HTTP error."
The changes are, of course, aimed at your convenience. But like all changes, these would create problems in the short run. In case you face any problems with your Site map, get in touch with Google Group.