First of all: I am a 100% beginner, never used Unity in my life until now. I was using this tutorial:
Around 8:45 in this video, he is about to test the game by pressing play. I followed all of the steps exactly, but I got this error for Platformer Character 2D (script): The associated script can not be loaded. Please fix any compile errors and assign a valid script. I am using Unity 5.1.2f1 (64-bit).
What is the error printed in the Console window?
This:
Assets/Standard Assets/2D/Scripts/Platformer2DUserControl.cs(3,27): error CS0234: The type or namespace name CrossPlatformInput' does not exist in the namespace UnityStandardAssets’. Are you missing an assembly reference?
Bump 
You will need to import the folder CrossPlatformInput from the Unity Package that was used in the video as well.
Alright, I added it, now what? I still get the error 