XML Parsing Error: not well-formed

Recieving the following error:

XML Parsing Error: not well-formed
Location: http://mydomain.com/sitemap.xml
Line Number 11, Column 55:		<loc>http://mydomain.com/?post_type=csshortcode&p=2860</loc>

I've tried renaming and rebuilding .xml file, but the results are the same.

Any help appreciated.