You must indicate in Turbotax that you do not have custody more than half the year, that you do have a custody agreement, and you do have a signed form 8332. This will create a situation in turbotax where you can claim the $2000 child tax credit, but you can't use the child to qualify for head of household status, EIC or the dependent care credit, because those benefits always stay with the parent will custody more than half the year and they can't be transferred even under a court order.
Your ex should indicate they have custody but they released the dependent.
If both parents make the correct selections in their tax program, both parents can e-file without a conflict. Either you or your spouse made a mistake, whether accidentally or deliberately I can't say.
Make sure your dependent settings are correct and try e-filing again. If you are blocked, file by mail and attach the original signed form 8332. Keep copies for your records. The IRS should process your tax return with the claimed refund. If there is a conflict with your ex, the IRS will investigate, but that usually takes 9-12 months.
