Google is giving me "unsupported file format" error with sitemap

[theslygoose]

Hello,
This has happened from 2 different sitemap generators now.  Google is saying unsupported file format, check again.  I'm pretty sure I did everything right but as I like at the /sitemap.xml page of my site I see there is no header, in which they require in their guidelines section.  Can someone look at it?

[XML-Sitemaps Support]

Hello,

what is your sitemap URL?