Because of how long this has gone on, correcting this is not simple by any stretch of the imagination. It requires IRS Form 3115 be filed. The 3115 is not simple and requires professional help. Especially if your state taxes personal income since that doubles the work required to fix this. I would suggest that if possible, you have the CPA who created the error be the one to fix it. Since it was their mistake, I'd fully expect there to be no charge for them to fix their screw-up.
