Package import crash.

I accidentally imported a large package into my project and it crashed. When I tried to open it again a window popped up saying,

'Fatal error!

Detected multiple Library folders within your project.

Did you copy a project into this project? Use “Export Package” to move assets between projects.

You need to remove the following Library folder(s) from your project before you can open it again:

C:/Users/MyUserName/Desktop/FolderName/FolderName2/FolderName3/FolderName4/unity/Assets/FPS/FPS_Tutorial_Completed/Library’

How do I do that?

Well, the error message you get tells you to remove …/Assets/FPS/FPS_Tutorial_Completed/Library. Looks like you have dragged and dropped the FPS_Tutorial_Completed directory in by mistake. Just go to your Finder or File Explorer and delete at least the Library folder. You do this outside of Unity, and preferably when Unity is not running.