Google Sitemap: Sitemap.xml is fine, but Google says 404

I’m using XML Sitemap Generator for WordPress 3.0b6.

I’m able to create a sitemap (both the .xml and .xml.gz versions). When I access https://seomate.info/sitemap.xml it works just fine. I even get the XLS stylesheet applied for free ??

However, when I want to submit my sitemap to google it says:

General HTTP error: 404 not found
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’ve tried a XML Sitemap Validator and the sitemap was found okay there.

Any clues on what is causing this problem?

The domain is pretty fresh (about a 12 hours now). But the site verified fine by creating a random-named file. So, why won’t the sitemap work?