It looks like your model likely doesn’t have joints (that is, an armature), and thus isn’t considered to be an Actor.
But this hasn’t happened before, does that mean the model is broken?
That depends on whether you expect the model to be animated or not. If not, then it may simply be that you’re attempting to load it as an Actor, rather than as a static model. However, if you do expect the model to be animated, then it may indeed indicate a problem with the model.
Well, okay, then I understand, thank you very much!