The default install of K3b doesn’t include mp3 support. So if you are trying to create an audio CD from a bunch of MP3 files then it’s a no go. Luckily the solution is as easy as installing an additional package. Launch the Synaptic Package Manager form the System -> Administration menu. The package you need to install if your running Ubuntu 11.04 “the Natty Narwhal” is libk3b6-extracodecs. After installing restart or launch K3b, and bingo MP3 support is available.