and the rejection Code and message says...............?

Code IND-116-01

This return has been rejected by the IRS because there is a dependent that is marked as eligible for the Child Tax Credit, but IRS records indicate that the dependent is too old to qualify for this credit.

In the Error Resolution it says to verify Relationship (but does NOT list PARENT in the list)

76 Year Old Parent who lives with tax payer listed as N-Non Qualifying Person; O-Other Dependent; with the box checked as NOT Qual for Child Tax Credit.

I have tried submitting with the other box checked as NOT Qual Credit Other Dependent and also WITHOUT the box checked as NOT Qual Credit Other Dependent.

I have previous clients and previous tax years where there has NOT been a problem.

Is the $500 dependent credit really going to make a difference on the return? What does it change the return to if she is taken off? that would clear your error. 

Maybe there's a gremlin in the data that needs exterminated --try deleting the dependent information completely (right mouse click, Delete Line in Table)  and  then re-enter the dependent information

@ljr  really ?    give up $500 !!