A Unity ID allows you to buy and/or subscribe to Unity products and services, shop in the Asset Store and participate in the Unity community.
Separate names with a comma.
I think one of my friends got this error too. He opened task manager and there was a stray Unity task open. End that task or restart your computer.
I know this is old but you can use SceneUtility to do what you want (https://docs.unity3d.com/ScriptReference/SceneManagement.SceneUtility.html)....