Blog List question

At the bottom of my blog is a list of other blogs. I REALLY like it b/c it shows the most recent posts... so it's easy for me to be able to tell who's posted. HOWEVER, not everybody is on it b/c it gives me this error on many of your blogspots I try to add:

"The page at http://www.blogger.com says: Could not detect a feed for this URL. Blog posts and update time will not be shown. Add URL anyway?"

DOES ANYBODY KNOW WHY? OR WHAT TO DO SO THAT THIS DOESN'T COME UP AND I CAN ADD THEM?