I have a Text box on a form:
private void button1_Click(object sender, EventArgs e)

{

textBox1.Text = "two";

}

I run (F5) the app and tried to modify the source code to:

textBox1.Text = "one hundred";

when debugging, I got the pop up box saying:

"Changes are not allowed while code is running or if the option

'Break all processes when one process breaks' is disabled. The option can
be enabled in Tools, Options, Debugging."

I have checked this option is already checked.