In order to prevent this error, you have to stop Chrome and it's services from running in the background.

Click on the menu symbol on the top right.  Looks like this -> Chrome menu

Click Settings

Scroll to bottom, click Show Advanced Settings

Scroll to bottom again, System, make sure Continue running... is unchecked as seen below

Bring up the tasks icons by clicking the arrow next to your clock.  If you see a tiny Chrome icon in there, right click it, UNCHECK Let Google Chrome run in the background

Close all Chrome browsers (logging out and back in may be the easiest way to shut them all down)

Open Chrome and log into Gradebook