Google Webmaster Tools giving file format error

Hi!

I just tested my sitemap in Webmaster Tools and it gave this error:

Unsupported file format: Your Sitemap does not appear to be in a supported format. Please ensure it meets our Sitemap guidelines and resubmit.

I just have a single sitemaps.add statement that adds all my publicly-accessible routes, and the generated file looks correct to me (you can see it here: https://modtest.canlio.com/sitemap.xml).

Any ideas on what I'm doing wrong?

That's strange. Unfortunately with Google Webmaster Tools, I think you can only run them against sites you own. Is there any more info it gives?

I googled for "google sitemap validator" and ran your sitemap through it, and it looked all good. Also Chrome opened it without errors. Wish Google Webmaster tools could be more specific. Is there nothing else on the page pointing to the exact nature of the problem?

No other information was given. Here is a screenshot of everything it says. You've never run into this before?