Docker: could not read CA certificate

I had the same issue. The problem was, that I upgraded from Docker Toolbox to Docker for Windows. When you uninstall Docker Toolbox, the user-specific env variables get not removed. The following did the trick for me:

1. Uninstall Docker Toolbox.
2. Uninstall VirtualBox (You cannot use VirtualBox, as it is necessary for Docker Toolbox and Hyper-V [used by Docker for Windows] at the same time.)
3. Remove the Docker Toolbox env variables:
   • Go to Control Panel\All Control Panel Items\System.
   • Click Advanced system settings
   • Go to Advanced Tab and click Environment Variables.
   • Delete all DOCKER_* entries from System/User variables.
     • DOCKER_TLS_VERIFY
     • DOCKER_CERT_PATH
     • DOCKER_HOST
     • DOCKER_TOOLBOX_INSTALL_PATH

4. Remove DOCKER_* from command-prompt or PowerShell. Run these command in PowerShell:

   [Environment]::SetEnvironmentVariable("DOCKER_CERT_PATH", $null, "User")

   [Environment]::SetEnvironmentVariable("DOCKER_HOST", $null, "User")

   [Environment]::SetEnvironmentVariable("DOCKER_MACHINE_NAME", $null, "User")

   [Environment]::SetEnvironmentVariable("DOCKER_TLS_VERIFY", $null, "User")

   [Environment]::SetEnvironmentVariable("DOCKER_TOOLBOX_INSTALL_PATH", $null, "User")

5. Restart PowerShell. (If necessary, restart system as well.)

Sources:

• Fresh install – could not read CA certificate. The system cannot find the path specified.

• [Docker for Windows] Certificate Error Solution