error message in feed

Hi
I get this message:

This page contains the following errors:
error on line 78770 at column 12: Extra content at the end of the document
Below is a rendering of the page up to the first error.

The facebook catalogue makes an issue out of this and reports this is not an XML feed.

I don’t want to publicly post a link to the feed, where could I send this to?

How do we proceed?

Thank you for the help