Within the traditional view of heaven there are two principles that are traditionally accepted as true. The claims are:

Agents in heaven have free will.
Agents in heaven cannot sin.

These two principles, however, entail a paradox. If an agent has free will, they are capable of sinning. Here is an argument based on this paradox against the traditional view:

If an agent has free will, then they are capable of sin.
Agents in heaven have free will.
Agents in heaven are capable of sinning. (MP 1, 2)
If agents in heaven are capable of sinning, then the traditional view of heaven is incorrect.
The traditional view of heaven is incorrect. (MP 3, 4)

Premises 3 and 5 are logically entailed from former premises, so I will not direct objections towards them. To object to 4 and 2, you must assert that the traditional view of heaven is mistaken. I choose to accept the traditional view, but I will not lay out an argument for why in this post. This leaves only premise 1 to be considered for an objection. As you may have guessed, that's exactly what I will do.

As it pertains to our earthly existence, our free will allows us to sin. We are presented with moral dilemmas, and often we choose to engage in the morally evil option. However, this is only the case because there are evil options on earth. Heaven, however, is a perfect place, and therefore evil does not exist. Heavenly agents will have free will, but their decisions will always be between two trivial or two morally good options. For example, when I am at a barbecue, I am free to choose whether I want a hamburger or a hotdog, yet neither is sinful; they are both trivial options. Further, one could choose to pray for their family or friends; both decisions are good. Perhaps these are the types of decisions that are made in heaven. Because of this, we can conclude agents in heaven can have free will and be incapable of sin. Therefore, premise 1 is false.