Dear Joost & dear wp friends, I've a problem whit your fantastic plugin.
I ran a test with google's webmasters tools and I noticed that my sitemap isn't working properly. I use the last version of wordpress seo 1.4.18 whit WP 3.6.1.
One of the mistakes is: "It seems that your Sitemap is not in a supported format. Verify that meets our specifications to the Sitemap and resubmit."
How can I fix the problem? I also tried to reinstall an old version, but the problem remains.