You may come across an error message titled "Unknown news site" in Webmaster Tools when you submit your news sitemap. The error says:

Your Sitemap is on a site that is not in the Google News database. Google News can only accept Sitemaps from sites that we crawl. If your site is crawled by Google News, please check that the URL of your Sitemap agrees with the URLs of your articles as they appear on Google News, including any leading "www". [...]

There are only a few issues which may trigger this specific error message and these are:

• You didn't suggest your site for inclusion yet. In this case go ahead and suggest it here

• You submitted your site and it was accepted for inclusion very recently (i.e. yesterday). In this case just wait a few days until the news related settings propagate on Google's end

• Both your www and non-www version (i.e. www.example.com & simply example.com) of your site is active, you suggested one of them, but you try to submit a news sitemap in which the URLs point to the other one.

For example: You suggested the simple example.com for inclusion and in your sitemap the URLs point to pages like http://www.example.com/article1.html

• Your website was removed from the news publisher database

If you didn't already, update your news sitemap to the new specification to have greater control of your article's indexation.