Descriptions of some other status lights and what they mean:

No power 
Plug in a power cable

Broken
If both LED lights are flashing red, it means the player is broken. Contact support for help.

Recovery is ongoing
The left LED will show a solid orange light while the right LED will show a solid red light while it's recovering. Don't unplug any cables and wait for the player to connect. 

Set up failed
The right LED will flash orange if the player is not paired to a location, or if that location is yet not activated. See here for guidance. 

Music is playing
The right LED will show a solid green light when music is playing. Music will still play for up to 30 days even if the connection is lost. 

No sound
The right LED will slowly flash a green light if the music is paused, no music is assigned and/or volume is set to 0. This can easily be fixed, just follow these steps.