Bar code in Smartform

I have to make a change to a field in a smartform. I need to change the character to 'Bar Code'. There are other fields on the form that are already Bar codes. My problem is it is not letting me choose a new character format 'BC Standard bar code (3 out of 9)'. Even in change mode.

What may I be doing wrong that it does let me change the character format?

Thank you.