That code indicates that your dependent has been claimed by other taxpayer. If someone else claimed your dependent, you cannot efile, you will need to print and mail the return.
If the dependent filed, and did not select "Someone else can claim me" and "Someone else will claim me" the dependent will need to amend the dependent's return so that you can claim the person as your dependent.
Still, the return will need to be printed and paper-filed (mailed). Once a social security number has been claimed, a return claiming that same social security number cannot be efiled.
https://ttlc.intuit.com/replies/5662008