This info looks right, which means your problem can be any number of places.
Did you record the music in 16 bit, stereo?
Is the music file in the missionname\music folder
Do you have a music folder?
Is your music volume turned up?
How are you playing the music? Through a trigger or the playmusic command.
Did you reload the mission in the editor after you added ,or made changes to, the description.ext file?
As you can see, the list goes on and on