What does it mean my daughter’s social security number is a duplicate?

Was you e-file rejected with that message?  That means that someone has already used your daughter's SSN on a tax return this year, and you cannot e-file with her SSN on your tax return.   Is she a teenager or a student who filed her own return?  Or is there another parent or person who might have claimed her as a dependent?  If you can claim her, and your return is being rejected, the only way you can file your own return now is by mail.   Print, sign and date your own return in ink, and mail it in.  The IRS will sort out the duplicate use of her SSN.

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.

Federal and state returns must be in separate envelopes and they are mailed to different addresses.  Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.