Ok so I have this problem on my phone where when I am playing music it won't continue to the next song unless I his pose then play which can become a hassle after awhile, but the thing is, its not only when my phone is locked it also does it when its unlocked, but a pop up appears when trying to go to the next song saying unable to play this song, but it plays the song if I pause the music then play it, I'm not using the Google music app but the music player that was on the phone.

Please help!
Thanks in advance.