Receiver won't play most radio streams

As the title suggests, my receivers (the other players work fine) won't play most radio stations. A few do play, for example, Radio Paradise and Secret Agent. There's nothing in the logs, but the Controller displays "Time out" while iPeng doesn't show any messages. I think it's the mp3 radio stations that do not work, but the sample pool is rather small. mp3-podcasts play without problems. I never changed this how-to-decode-this-or-that-file-format config file and I am a bit of a loss here.