Programmatic button click throws 'System.StackOverflowException' exception

I have written a WinForms program in C#.Net to click a button programmatically within a password form.

Form1 loads and shows Form2 as a dialogue box.

The application will close if DialogResult is anything other that DialogResult.OK.

So far I have a button click event, which is coded as follows:

 if (txtpass.Text == "")
            {
                MessageBox.Show("You need to enter a password", "Password", MessageBoxButtons.OK, MessageBoxIcon.Asterisk);
                txtpass.Focus();
            }
            else
            {
                if (txtpass.Text == "1234")
                {
                    radButton1.DialogResult = DialogResult.OK;
                    radButton1.PerformClick();
                }
                else
                {
                    MessageBox.Show("Password Incorrect", "Password", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    txtpass.Text = "";
                    txtpass.Focus();
                }
            }

I use radButton1.PerformClick();, but running the program gives me the following message:

An unhandled exception of type 'System.StackOverflowException' occurred in mscorlib.dll

I'm unsure what is causing this exception to throw.