I wanted to let you know in cauase you have the same problem I did today.
Today I launched a new website on MODX Revo. From subdomain.domain1.com to domain2.com
The HTML version of the sitemap didn't work and gave me an error: sitemapfriend.error.loading class
What I did to solve:
A reinstall didn't work so I removed the add-on sitemapFriend and installed it again.
It's pretty cool to have a clickable sitemap on your website and have a sitemap.xml for Google Webmaster Tools.
Cheers
