Downloading EV3 programs: Error code 0
Yeah... It happened to me this very day...

SOLUTION:

One of the following always does it (listed in descending order of effectiveness):


Relaunch the EV3 Software (Be sure to save your work!)
Use a Download Cable instead of Bluetooth
The EV3 Software messes up on Windows 10; try using an older PC.
Restart the brick.
Restart the computer.
Try turning bluetooth on and off