You are likely being required to mail your state tax return because your daughter's Social Security Number (SSN) was already used on another tax return. Click here for How do I file my return by mail?
This would cause your e-filed return to be rejected. You should receive a letter from your state requesting additional information.
This usually happens to prevent identity theft or other fraudulent claims for dependents. It requires the state to review documentation to verify who has the right to claim the child.
If your spouse or partner or someone else claimed your daughter first, the IRS/State system will automatically reject your electronic submission to prevent issuing the same refund/credit twice.
When filing by mail, you are able to attach proof that your dependent lived with you more than half of the year and any court documents you may have showing you are the custodial parent.
If you have additional information or questions regarding this, please return to Community and we would be glad to help.