Android AVD throws errors, such as "Failed to sync vcpu reg" How do I fix “Failed to sync vcpu reg” error? does not help. I tried all the solutions I could for Mac on the post but none worked.

I started a new project and tried to run the emulator, but I get these errors:

HAXM is working and emulator runs in fast virt mode
emulator: Failed to sync vcpu reg
emulator: Failed to sync HAX vcpu context


It used to work yesterday. I didn't change/download anything. 

Why did it stop working? I also made sure there are no other processes of the emulator running.

I'm running Android Studio in OS X Yosemite.
Make sure that you're not running any other virtual machines, then try again.

I was running a guest Windows 8 VirtualBox on El Capitan and I got the same error when I tried to run a virtual Android device in Android Studio. I shutdown the guest OS and VirtualBox then my AVD booted up.