Checking inheritance#

Components and ScriptableObject scripts must inherit from MonoBehaviour and ScriptableObject.
If a user type does not inherit from MonoBehaviour it cannot be attached to a GameObject.
If a user type does not inherit from ScriptableObject it cannot be instanced as a scriptable asset.

Resolution#

Ensure your class appropriately inherits from MonoBehaviour or ScriptableObject, or a suitable subtype.

public class ClassName : MonoBehaviour

My script still cannot be loaded.