[Plugin: WordPress SEO by Yoast] 404 when viewing xml sitemap

WordPress version: 3.4.1
WordPress SEO version: 1.2.5
OS: Windows Webserver

I did this:
Activated the plugin and via admin panel opened the XML sitemaps.

I expected the plugin to do this:
Show a list of XML sitemaps.

Instead it did this:
Show a 404 server error (file or directory not found).

I have this problem with two websites, and have it working with one but I don’t know why that is. The same versions and same configs. Can it be a specific IIS user config? Read access? Please let me know if you need more info.