MaskedTextBox.SelectAll on GotFocus doesn't work with mouse

Your SelectAll() is being overwritten by the default functionality of the masked textbox select. I would use the Enter event, it allows for tabbed entry or mouse click entry to the masked text box. You will most likely need to use the BeginInvoke method. Try the code below. It worked for me when I tried...

private void maskedTextBox1_Enter(object sender, EventArgs e)
{
    BeginInvoke((Action) delegate { SetMaskedTextBoxSelectAll((MaskedTextBox) sender); });
}

private void SetMaskedTextBoxSelectAll(MaskedTextBox txtbox)
{
    txtbox.SelectAll();
}