Seems like the most common problem people have talked about already inhere...
You prob. use it locally and didn't register your domain-name you use for it. Once you register the domain-name the MP3 module will work (this blahblah is based on 4.1.2 but prob. is the same in 5.0)
Use Search with keyword MP3 in this forum and you see all that has been said already.
Grtx, Harro