I imported Cinemachine for my 2D project and itnworked for a while, but when I started it up today, this message popped up on all Cinemachine scripts: Imgur: The magic of the Internet
Try deleting the CM folder and reinstalling. Looks like the CM script got deleted somehow.
The forums are the best place for CM related questions: https://forum.unity.com/forums/cinemachine.136/