You do not mention your son's age, nor do you mention if he lives with you. Go back to MY INFO, delete him as a dependent and then re-enter his information, going very slowly and carefully through EVERY screen. Do not skip past any screen.
IRS interview to help determine who can be claimed:
https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**