Setting the default program to open mp3 files didn't work for me. I ran Musicbee in admin mode, selected proper association. All other music programs work without trouble: VLC, Groove, Media Player, etc. The easiest solution for me was to uninstall the program. Shame.. it looked promising at first but this is a deal killer. Maybe I'll look into this in the future or if someone can post the solution here, I'll revisit the issue at a later time.