error on line 3 at column 6: XML declaration allowed only at the start of the document Below is a re

What would cause these error when pulling up the subsites sitemaps. We are using domain mapping, but it errors on both the subsite domain and the redirected one.

This page contains the following errors:

error on line 3 at column 6: XML declaration allowed only at the start of the document
Below is a rendering of the page up to the first error.