“If I've gotten everything in me from God and He hasn't given me the ability to make errors, it doesn't seem possible for me ever to error. (Descartes, Meditation IV: On Truth and Falsity).”
The framework of his arguments center on the Great Chain of Being, in which God's perfect goodness is relative to His perfect being. On the extreme opposite end of the scale is complete nothingness, which is also the most evil state possible. Thus, humans are an intermediary between these two extremes, being less "real" or "good" than God, but more "real" and "good" than nothingness. Thus, error (as a part of evil) is not a positive reality, it is only the absence of what is correct. In this way, its existence is allowed within the context of a perfectly inerrant God.
I find that I am "intermediate" between God and nothingness, between the supreme entity and nonentity. Insofar as I am the creation of the supreme entity, there's nothing in me to account for my being deceived or led into error, but, inasmuch as I somehow participate in nothing or nonentity — that is, insofar as I am distinct from the supreme entity itself and lack many things — it's not surprising that I go wrong. I thus understand that, in itself, error is a lack, rather than a real thing dependent on God. Hence, I understand that I can err without God's having given me a special ability to do so. Rather, I fall into error because my God-given ability to judge the truth is not infinite. (Descartes, Meditation IV: On Truth and Falsity).
Descartes also concedes two points that might allow for the possibility of his ability to make errors. First, he notes that it is very possible that his limited knowledge prevents him from understanding why God chose to create him so he could make mistakes. If he could see the things that God