I resubmitted the Sitemap in the Google webmaster tools section and it came back roughly 10 - 15 minutes later with the error. I just checked back and the information was the same.
I thought you were really on to something there. I did go in and found my module was not activated. Have since activated it, but, I resubmitted the Sitemap on Google and I get exactly the same error.
The only response coming back in the webmaster tools/Sitemap details is "Unsupported file format - Your Sitemap does not appear to be in a supported format. Please ensure it meets our Sitemap guidelin ...