Summary:
Sitemap uses older schema .84
Detailed Description:
Sitemaps only need the following urlset as per the site map protocol at
http://www.sitemaps.org/protocol.php
Use this:
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
Instead of this:
<urlset xmlns="http://www.google.com/schemas/sitemap/0.84"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.google.com/schemas/sitemap/0.84
http://www.google.com/schemas/sitemap/0.84/sitemap.xsd">