Objectivism, even in it's name posits the notion that individuals essentially have a God's-eye-view of the world, or at least that they are capable of such. (In that regard it is simply a species of that great heresy, modernism). That is, they stand over against the world observing it and forming impressions from a purely objective standpoint. This is flatly false, and is a rejection of the creator/creature distinction fundamental to the Christian worldview (Rand was an outspoken atheist). Human beings, as created beings, find themselves within the world, and thus apprehend it as subjects. That is to say, all human knowledge is subjective. It is mediated through an I, a subject. We cannot stand above creation looking down, with a God's-eye-perspective and simply relate to the world as object. Yes the world is full of objects, but I am one of them and I apprehend it from within. I cannot escape myself to see things "as they are." I see them as myself, through my own grid of knowledge, awareness, experiences, etc. I perceive the world from a particular, and yes, subjective perspective. I apprehend reality in a finite manner. This is not to deny truth or real knowledge, it is simply to recognize my place as part of God's creation, and not possessing a view from without.
Further, this does not deny that we can know true things, or even that we can know the world 'as it is,' in one sense. Although I am a created being, I am one created in God's image. Furthermore, this same God created me for this world, and has blessed me with the ability to apprehend it as such. However, knowledge is always mediated. Once again, I do not have a God's-eye-view of the world, as if it were a system I were standing outside of; rather, from my place within creation I receive revelation from God. God reveals himself through creation, and more directly through his Word spoken and written by his chosen instruments in Scripture. So indeed, I can have true knowledge, and accurate knowledge, but not "objective knowledge" in the strict sense. I am in fact, ever a subject.
This is really just a short version of a long way of saying that Objectivism is wrong precisely because it is founded on a non-Christian epistemology that does not take knowledge to be a gift from God, but a thing to be grasped by men and women who fancy themselves gods.