I connected my earphone and when I tried to change the volume, I got a prompt like
Except that there was a small "cancel" icon in it (like this). I could not change the volume. I had to unplug and plug again the earphone.
What does that mean?
OSX Yosemite. Macbook Pro Retina Display, Mid 2014 model.
Intel High Definition Audio
under System Report, yes.