could not read CA certificate "C:\Users\username\.docker\machine\machines\default\ca.pem": open C:\Users\username.docker\machine\machines\default\ca.pem: The system cannot find the file specified.
This problem occurs when Docker Toolbox installed and uninstalled install Docker for Windows computer, or installing Docker for Windows when choosing Windows container, use the command appears Docker error can not find the CA certificate
This problem is because of the write environment variables when you install Toolbox, and the path of the certificate is to configure the environment variables, environment variables still unloading time
So Right My Computer -> Properties -> Advanced System Settings -> Environment Variables -> user variables, put the number of Docker * environment variables all deleted
Open a command line window re-execute the command, you found use.
Reference Links: https://www.jianshu.com/p/ee26539036aa