That's one of the weirdest error I've seen yet as it still works for me However, you may want to feedburn your source to ensure it's not a problem between your fetching server (your local yahoo one) and eventbrite.
Sorry for the delay in the answer, I have been very busy.
As I was able to get the results, I don't think EB changed their settings, nor do I think it was pipes. It has to be a local thing, so I'm thinking maybe the use of pipes with EB increased in your part of the world, and there were some traffic issue.
Actually as it works for you now, I'm thinking that what worked is that now it's the feedburner user agent which queries EB instead of Yahoo pipes'. It a recurrent issue with popular websites: as the same user agent is used for all pipes of a given Y! server, websites see a lot of traffic from one single virtual user.
To conclude, with your feedburner solution, no more problem in perspective :)