There are two kinds of camera errors.
In both cases, the most important thing is to make sure the camera is connected directly to the computer (not through a USB hub) and that it has enough power supply.
*Make sure that your camera is supported by the Mirror Me software (list at the bottom of this article).
*Make sure that your camera is detected by the computer (Control Panel > View Devices and Printers). If using T6\T6i - make sure that the WiFi option is disabled.
1) Move the focus switch to manual (MF) like in the picture above. If it already is on MF - focus your camera:
a. Switch to AF
b. Take a picture while focusing on a large object or a person.
c. Switch back to MF.
You can also see this article for assistance.
2) Make sure the camera is on M (Manual) mode:
3) Make sure the "Image Quality" setting is not on "Raw" in the camera's settings menu. If so, switch it to S2:
If you need any help with changing your camera settings, you can see this video for assistance.
4) Make sure the "Auto power off" option In the camera's settings menu is disabled:
5) Make sure you don't have an EOS utility software running in the background.
6) Try a different port on your computer.
7) Try to use a different USB cable.
8) Uninstall/Disable the anti-virus software installed on your computer (even if it already worked before).
9) Install VCredist files (attached at the bottom of this article).
*Make sure your event name doesn't have any special characters in it and written in English letters only. Add a new event named "test" and try again.
Advanced: In the Device Manager you have an option to prevent windows "Power Management" from allowing the computer to turn off the device to save power in the device manager.
a. Open "Device Manager"
b. Right-click on USB Root Hub.
c. Remove the selection from the "Allow the computer to turn off this device to save power" box.