OnCollisionEnter2D not responding from runtime?

I have a building object that stays in place. It has a RigidBody2D and a BoxCollider2D.
I have an object that moves towards it. This object has a BoxCollider2D.

When they collide, the OnColliderEnter2D function should be calling on the moving object? Did I set this up correctly?

I am loading these objects in runtime through a script that loads the objects positions on the screen. Could that be detaching them?

Okay! So the layout I explained above WILL work. Somehow, I stopped adding my collider to the moving object in script. Everything is back to normal now.