Disabling a checkbox when another checkbox is clicked

I am trying to disable the thin and crispy checkbox when traditional checkbox is clicked. I have these in a group due to me enabling the whole group when the numericUpDown value is set to 1. When I click traditional checkbox, it doesn't disable the thin and crispy checkbox. I am using windows form application

Code

        private void NudQuantity1_ValueChanged(object sender, EventArgs e)
        {

            if (NudQuantity1.Value == 0)
            {
                gbCheesePizza.Enabled = false;
            }
            else
            {
                gbCheesePizza.Enabled = true;
            }

            if (CBXTraditional1.Checked == true)
            {
                CBXthinandcrispy1.Enabled = false;
            }

        }

When I run this code outside of a groupbox, it works perfectly.