You need to go into the settings, and add in your MP3 License, which on there is a link on where to get it at. Its only 5 bucks.
Log into Centova Panel > Settings > Auto DJ tab
You will see 2 boxes there.
MP3 unlock name
MP3 unlock code.
After adding that information in, Click on the Mount points tab, highlight /stream (or whatever you have listed in there) > Auto DJ Settings
And in the drop down for Audio Encoder, select MP3, and then click Update.
But in order for it to work, you must purchase the MP3 license.