I upgraded to the new Dynamic Headers version on this site:
http://equinecisers.com/wordpress/
and the message I got was the following:
Fatal error: Call to undefined function show_media_header() in D:\Hosting\2781642\html\wordpress\wp-content\themes\atahualpa342\header.php on line 49
I tried to delete the plugin (which hadn't even been activated), to no avail. I even tried to restore the old header file. That didn't work either.
So if this happens to anyone, revert to the old version of Dynamic Headers until there's a reply to this post.