I'm not an expert on XML so I don't know why this wouldn't work for you, but would work for everyone else.

Furthermore, there is no header in the file for text/html:

PHP Code:
<?xml version="1.0" encoding="UTF-8" ?>
<rss version="2.0" xmlns:g="http://base.google.com/ns/1.0">
<channel>
.
.
.
</channel>
</rss>