IND-517-02 - The second dependent.

We got the IND-517-02 rejection code.

I'm trying to confirm that that means it's the second dependent listed on our return. When we first got it, I assumed it was my son who recently filed his taxes incorrectly indicating that no one else can claim him as a dependent. 

However, if, as I believe, the 02 means that it's the second listed dependent, that indicates it's my daughter -- who doesn't file taxes.  

I know in either case we now need to print and file by mail -- but can someone confirm my understanding of the code so that I can take the appropriate steps.  Is there anyway my co-filing wife could be "01" and my son "02"?