Hi, I verified that it's not working for me either. I have used Atom feeds in the past, and since it was working for you previously, my guess is that something must have changed in the feed structure to make it noncompliant with the standard, or at least outside of what's expected by Feed Manager's processing engine.
When I pull the feed up in IE 8, the feed declaration is
<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
Per Wikipedia, for an Atom 1.0 feed it should read:
If that site has any kind of support mechanism, you may want to ask them if there's anything they can do on their side to get the feed back into spec. You could also try running the feed through Yahoo Pipes. That may be able to parse it out and it will output a standard RSS feed that is consumable by Feed Manager.