Problem with Google Webmaster tools not finding Google XML Sitemaps

Hi I have been using Google XML Sitemaps plugin. I have noticed in the webmaster tools that the site map didn’t work as the sitemap’s path was http://example.com/sitemap.xml whereas google was looking for http://www.example.com/sitemap.xml. So in the settings I added www and the sitemap was detected. However I now get this for every page
“Paths don’t match
We’ve detected that you submitted your Sitemap using a URL path that includes the www prefix (for instance, http://www.example.com/sitemap.xml). However, the URLs listed inside your Sitemap don’t use the www prefix (for instance, http://example.com/myfile.htm).”

How do I change the path of each so that google can find it?
Thanks in advance!