Dashboard Feeds error

Using the Dashboard Feeds plugin for my WPMU network. I enter my feed URL as http://www.driverevenue.marketing/feed/ (which is the actual XML feed) and get the following error message:
RSS Error: A feed could not be found at http://www.driverevenue.marketing/feed. A feed with an invalid mime type may fall victim to this error, or SimplePie was unable to auto-discover it.. Use force_feed() if you are certain this URL is a real feed.

This feed is on a Wordpress site that is NOT part of the WPMU network. How do I proceed from here to show my feed on every site in my WPMU network? Thanks.