The player queue is full
The queue count must be
< 20="" to="" add="" tracks.="" when="" the="" queue="" is="" less="" than="" 20,="" you="" can="" add="" (with="" one="" click)="" any="" track,="" an="" entire="" performance,="" even="" a="" complete="" multi-cd="" album,="" or="" add="" the="" start="" of="" a="" continuous="" radio="" stream="" to="" the="" player.="">