Simply Importing Assests Breaks my Unity Game

I'm working on a networked Unity FPS based off of this tutorial/project: http://www.youtube.com/watch?v=eKHLpWEWlMI

and my issue is that when I attempt to import something into the scene, the Main Camera no longer becomes the child of the newly created First Person Controller and instead just floats in the air.

I'm not sure what is causing this as I'm not adding anything into the scene or even changing anything, only importing assets.

Any help would be greatly appreciated.