It seems that if your site has over 50,000 posts, google will not accept the sitemaps coming from your site unless each of the sitemaps are <50k urls. I have tested this out through Google Webmaster Tools and manually chopped them into two smaller files and google took it in without a problem.. but that's manu process. Can you please fix this ?
Here is the exact message.
Too many URLs
Your Sitemap contains too many URLs. Please create multiple Sitemaps with up to 50000 URLs each and submit all Sitemaps.