Apple - Play/Pause/Prev/Fwd buttons not working

I found this to solve the problem for me, thanks to Major Hayden!

...check your keyboard shortcuts in Chrome:

• Choose Preferences in the Chrome menu in the menu bar
• Click Extensions in the left sidebar
• Scroll all the way to the bottom of the page
• Click Keyboard Shortcuts
• Look at the key bindings in the Google Play Music section
• Remove them all by by pressing the 'X' icon next to them.