I had thought I needed to Annualize Income Installment Method and I filled out that portion, but now I want to delete it. How? Keeps bringing me back to it?

I have gone back and checked NO , don't want to Annualize, but when I try to complete the return it makes me re-visit Form 2210 saying "Check this Entry  Form 2210AI: Line 16-a must be entered" Then says "Line 18"  with an entry box for a number?