TurboTax has no way of knowing if your ex claimed your son. That cannot be what is causing your problem. There is no need to contact your ex about it.
You wrote "at the end it says he doesn't qualify." Doesn't qualify for what? Does it say he doesn't qualify as a dependent, or does it say he doesn't qualify for something else? What is the exact message from TurboTax, word for word?
Look at your actual Form 1040, not a TurboTax screen. Is your son listed in the Dependents section in the middle of the first page of Form 1040? If his name is there, then he was not dropped from your tax return.
