The sitemap produced looks fine to me, having read Google's schema requirements, but when submitted, either manually at the webmasters Google site in my account, or by automatic ping, I get the report...
We were unable to read your Sitemap. It may contain an entry we are unable to recognize."
I tried changing the <?phpxml... opening tag to just <?xml...> but that made no difference. It's encoded correctly.
I can't see what their problem is but also I don't know how to validate the XML (using the command line tools Google recommends) to find out. And in any case, of course I need the program to produce a valid sitemap.
The sitemap is at [external links are visible to admins only]