infinite seo issue

I am getting an error in the sitemap that is like this:

XML Parsing Error: not well-formed
Line Number 1628, Column 58:<loc></loc>

This is a sub-directory of a multisite network.

Also, on another site, the sitemap.xml is not present, whereas on another it is just right. I've looked through the documentation, and can't seem to find how to adjust the settings for each site in the network.