Strange SuppressKeyPress

[mrjohn]

Hi !
I have the following problem : I want to supress a key for a textbox :

If e.KeyCode = 66 Then ' B Key
            e.SuppressKeyPress = True
            e.Handled = True
        End If

this is working, B key is supressed,but adding just a messagebox will not work :

If e.KeyCode = 66 Then ' B Key
            e.SuppressKeyPress = True
            e.Handled = True
     MessageBox.Show("OK")
        End If

Why ?
Thank !