What do I do when I see "Security Error - User don't have permission 'ManagementConsole'"

Question:

I'm getting following error in the backoffice:

Answer:

Besides that you are logged to the backoffice with your backoffice user, you opened in the same browser also the game. The session was overwritten with the player's credentials and the player doesn't have permission for the backoffice. 

You cannot use the backoffice and player in the same browser. Open the backoffice in different browser or in the incognito mode.