E-file rejected - dependent didn't indicated they could be claimed as a dependent

My return has been rejected by the IRS because "a dependent on this tax return, has filed their own tax return without indicating they would be claimed as a dependent."

 

My son accidentally filed this way. He then filed an amended return correcting it. Then I re-submitted our return and it was rejected again for the same reason.

 

How can I tell if it is he who is the issue or if it is another of my dependents? 

 

Are my taxes late now? Do I need to file an extension?