If there's more than one dependent on the return, note the "value" at the end of the rejection. You may want to write it down. It'll help you find the dependent causing the issue.
Go to the General folder.
Select the 1040 screen.
Open the
Dependent Information
statement at the bottom of the screen.
Look in the
SSN
field for the value referenced in the rejection. Once you find it, check for typos or incorrect information for the dependent.
If there was wrong information entered, correct it. Then re-create and retransmit the return.
If the data is correct, explain to the taxpayer that the dependent's SSN was already used and a paper return must be filed with Form 8948. Mail the return and attach all required documents (e.g. Form 8332, Release of Claim to Exemption for Child of Divorced or Separated Parents, copy of Divorce or Separation agreement or other supporting documentation).