I have added sitemap(_index|[0-9]+)?\.xml to the exclusions in W3 Total Cache as instructed on Yoast's website. (http://yoast.com/xml-sitemap-in-the-wordpress-seo-plugin/)
I have also added this code to my .htaccess code as described here:
However, Google is still pulling a 404 on my sitemap. When loaded into a browser, it's just a blank page.
I get this error in Google Webmaster tools:
We encountered an error while trying to access your Sitemap. Please ensure your Sitemap follows our guidelines and can be accessed at the location you provided and then resubmit.
I have also unchecked the boxes to ping Yahoo and Bing. I have also switched to the 2012 theme with NO other plug-ins activated and still am having this same issue. I am not sure what else to try here.