A really odd MissingReferenceException

I was absent from Unity for a while now and I am currently doing the tutorials to get myself back into the game.

When I was testing my scene, I encountered a MissingReferenceException. I check my codes for a few times but I just cannot get rid of the Exception.

After much frustrations, I created a DefaultScript with no modification made on it; I ran the scene and the same error message pops back up again.

Any thoughts on this issue?

Can you post your code, so we can get a better idea of what’s happening?