Tax law sucks...lol
You don't have a tax law problem. He does! As far as the IRS is concerned, he can't claim the child as any type of dependent unless you consent and provide him with a Form 8332. If he does and the IRS tries to resolve the issue, you win. Hands down.
Your divorce decree may require you to allow him to claim the dependent but that's not tax law, that's a local family court decision. The resolution to that is to go back to court and have the decree modified.
I agree with Macuser's statement when he said that if he thinks the IRS said that, he misinterpreted what they said. Alternatively he never asked but said he did, or the individual IRS person was wrong.
