flutter doctor - Error: Downloading Dart SDK from Flutter engine
This is how you can fix it :
Open Control Panel – System – Advanced system settingsand click on the button Environment Variables.
If environment variable ComSpec is set to anything other than %SystemRoot%\system32\cmd.exe expanding usually to C:\Windows\system32\cmd.exe, then reset it to Windows default %SystemRoot%\system32\cmd.exe.
This error occurs when you disable BITS [Background Task Infrastructure service]
type "Services" on Cortana then click on services > then go to >Background Task Infrastructure service> Enable and start it > Then reboot your laptop
It will help you to solve this error...
BITS related errors can be solved by just enabling Background Task Infrastructure service