Probably too many add-ons enabled.
That can happen?Whoa, and I thought I had a lot.
You can only have a maximum of 4096 datablocks. Once those are used up, new datablocks cannot be created. Music datablocks are created after the add-ons are loaded, so if you're not getting any music it's probably because you've used up all your datablocks in the add-ons.