sitemaps and seo wordpress mu no place to be seen after install

I feel like I've done everything right. Put files in the mu-plugins folder, updated the htaccess, checked that it had the recent change date, but there is no evidence of sitemaps or All in one Seo on my site (not in plugins, not at the bottom of add post pages, etc). When I test for sitemap get the following.

XML Parsing Error: no element found
Location: http://www.localhost.com/sitemap.xml
Line Number 1, Column 1:

Clearly I'm missing something, but I can't figure out what it would be.

I've installed domain mapping although I'm not sure that's working either...could that be an issue?

Leslie