I just watched this Video https://unity3d.com/learn/tutorials/projects/survival-shooter/player-health and tried to drag'n'drop the UI-Elements on the matching script, just like they did. But this is not working for me. If I hover the public field Unity shows up an error icon and I can't drop it there. If I set this UI-Element as prefab I can place it there, but it does not update the Element which is in the Scene when the Code is live. The Elements just gets an update after each restart. Can anybody explain to me why I cannot drag'n'drop my Object from the hierarchy to the public field?