Sitemap not found by Google Webmaster Tools

I've installed this plugin and I can easily see the sitemap via my browser at http://racshadow.org/sitemap.xml exactly as I would expect. AND it even produces the sitemaps for all the blogs in my network. Woot! Nice work, guys!

However... when I try to get Google Webmaster Tools to see the sitemap -- by submitting it to them -- the tool says it's not there. The error it returns is:

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 submitted it to them two ways:
at /uploads/sitemap.xml and
at /sitemap.xml

in the plugin, this is my setup, and both are visible to my browsers:
Path to the XML Sitemap -- /home/racreprt/public_html/wp-content/uploads/sitemap.xml
URL to the XML Sitemap -- http://RACShadow.org/sitemap.xml

Ideas?

I'm using WP 3.2.1 and all plugins are updated to current versions, as of today.