Yoast WordPress SEO sitemap part of the plugin not working on the root domain

I was changing the root domain on a multisite installation (and also getting rid of /blog slug from the root URLs with WP No Category Base – WPML compatible plugin) and I think it might have something to do with a Sitemap part of the plugin not working (it might be possible there is another reason too).

Please let me know if there is any way to check what is going on. I just get a blank window after clicking on http://domain-name.com/sitemap_index.xml

My root admin is not working properly also (I wrote about it in the previous post), so it might be one of the reasons too (I am not sure if there is a way to reinstall most of the files on the top of the old install etc, to get it all straightened up etc; or some other solution)

Thank you.