I have 2 children. One turned 17 in 2018. The other turned 14. My claim was rejected because I claimed my 17 year old as a dependent. However, I do not see how to fix this issue.
There should not be any reason why you can't claim your 17 year old as a dependent. See the rules below. If he incorrectly claimed himself, he will have to amend and you will have to mail in your return.
Relationship — the taxpayer’s child or stepchild (whether by blood or adoption), foster child, sibling or step-sibling, or a descendant of one of these.
Residence — has the same principal residence as the taxpayer for more than half the tax year. Exceptions apply, in certain cases, for children of divorced or separated parents, kidnapped children, temporary absences, and for children who were born or died during the year.
Age — must be under the age of 19 at the end of the tax year, or under the age of 24 if a full-time student for at least five months of the year, or be permanently and totally disabled at any time during the year.
Support — did not provide more than one-half of his/her own support for the year