I can see that it works now, but in case someone else is wondering, I’ll just post this anyways:
Do you have a speed optimization plugin, such as W3 Total Cache or WP Super Cache? This can be an issue with minification (Minify) settings. If you use any form of minification, you should ensure that your sitemap(s) are excluded.
For example, in W3 Total Cache, you go to the settings for Minify, then locate the box marked “Never minify these pages:” and enter:
([a-z]+)?-?sitemap.xml
([a-z]+)?-?sitemap.xsl
