Yes, it goes without saying, it makes no sense to describe how you got the object inside Unity. If you see there in an acceptable form - then it can be workable in the game.
But there are various hierarchies and parameters, tags that need to be observed. This can be checked only by seeing the settings of the prefab that is located in Unity editor.
It will be more useful to show exactly this. And, you have never published what is contained in the error message.
As i advised you in another thread - make a primitive object (cube, stick) and try to get it in the game, in your hands.
(do not use another fbx that you pulled out using AssetStudio!)
PS: You don't have to use the LODs. You can only use LOD0. Just remove the rest.