same issue here, had a show scheduled with three mp3 files. The shows before and after both, again, with mp3 files, played perfectly. But as soon as those 3 files were scheduled to play everything went off the air. Then came back up with the next show. I played each file locally and they are all recognized as MP3s. I tried this on 2 different icecast server one on ubuntu 12.04 server with the airtime installation on the same computer. And another on a fedora icecast server with the airtime server on a different box running ubuntu 12.04. Both airtime installations are 2.4.0
figured it out, looks like I have to convert the MP3s to MP3s. Soon as I did that they played while the "unconverted" MP3s caused airtime to go off the air. Oh BTW these "unconverted" MP3s played just fine on 2.3