Firstly this should be in the Plugins forum. I hope moderators will do the moving.
Now lets see your problem. You say that you have installed Music Logger Plus but itsnt working?
Possible things you can try.
1) If you didnt restart messenger after installation please do that.
2) Go to Plus! > Prefrences > Plugins and check if Music Logger Plus.
3) In the Plugins tab only, highlight Music Logger Plus and click configure and see it Log to Plus! is enabled.
I hope these helped.
Ill be attaching screenshots for this. Just would take me a while.