That is a familiar story---we get that a lot.
MY DEPENDENT SAID HE COULD NOT BE CLAIMED
Your dependent filed a return without saying he could be claimed on your return and your return was rejected? AFTER his return has been fully processed and he has received his refund, he has to file an amended return that says he can be claimed as a dependent on someone else’s return. Amended returns must be prepared on a Form 1040X. It takes the IRS at least four to six months to process an amended return.
Meanwhile, since your e-filed return has been rejected, you now have to print and mail it in to the IRS. You will not be able to e-file. You do not have to wait for your dependent’s amended return to be processed. Remember that when you mail a return, you need to include copies of your W-2, etc. with your return. Use a mailing service like certified mail that will track it so you will know that the IRS received it.
For your dependent:
See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
When they amend —The dependent needs to go to MY INFO, click their name, and go to the question that asked if they can be claimed as someone else’s dependent. The answer needs to be YES.