If your return was rejected due to your dependent's SSN being used on another return, the first thing to do is to verify that you entered the SSN correctly in the return. If it is incorrect, fix it and resubmit it. If it is incorrect, that means that someone did indeed use your dependent's SSN on a return. The IRS typically grants the tax benefit(s) related to dependents to the first taxpayer to file a return. It is not uncommon for a parent who qualifies to claim the child to have their e-file rejected because the child was already claimed by another taxpayer. If you qualify to claim the child under the law, file a paper return and claim the child as a dependent. This will start action on the part of the IRS to determine who actually qualifies to claim the child. You will receive mail from the IRS when they start this process. 

why doesn't my daughter count for the child tax credit?

because she's 17 years old  she had another disqualified situation she doesn't count for the child TAX. SHE IS LIVING WITH ME FOR 12 MONTHS I AM FULL OF CUSTODY OF HER IN MY LIFE.

The Child had to be UNDER 17 on Dec. 31 to get the Child Tax Credit.  See Child Tax Credit FAQ

https://ttlc.intuit.com/community/credits-and-deductions/help/what-is-the-child-tax-credit/00/25961

In order to claim the child tax credit on your 2020 tax return, your dependent has to be 16 or younger as of Dec 31, 2020.   Since she is over the age to claim the child tax credit, you should receive a credit for $500 (Credit for Other Dependents) on your tax return.   

To qualify for the Child Tax Credit, your child must fit all of these requirements:

• Be under age 17 at the end of the tax year
• Is your son, daughter, stepchild, foster child, adopted child, brother, sister, stepbrother, stepsister, half-brother, half-sister, or a descendant of any of them (for example, a grandchild, niece, or nephew)
• Has his or her own Social Security Number
  • Children with ITINs don't qualify, but may instead be eligible for the $500 Credit for Other Dependents
• Lived with you for more than half the year
• Didn't support him/herself (didn't pay more than half their own expenses)
• Is a U.S. citizen, U.S. national, or U.S. resident alien
  • Residents of Canada or Mexico wouldn't qualify

@Patricialy

I have 2 dependents and do not know which SSN is creating the rejection. It would be nice to know so I can address it. None of my dependents file taxes and their SSN's are correct. However, Turbotax says a number in brackets should tell me which dependent SSN is the problem [1] for the first listed or [2] for the 2nd listed. Where do I find that in Turbotax? Turbotax fails to direct me to where that can be seen in the software. 

Go into my information, then dependents, then edit. Here is where you shall be able to see their ss#'s and change whatever has to be changed. 

Nobody else has that you know of.

You are forced to file a paper tax return via US Mail.

@wolff_wyatt 

I’m having this same exact problem this year. How can I find the dependent that’s causing the issue?

If someone has used your dependents information on their return, you will need to mail in your return. You won't be able to efile. @Katisha352