Strange SuppressKeyPress

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

vb.net Code:

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 :

vb.net Code:

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

Why ?
Thank !

Frns.. Any one gone through this ?? today, I have also came across same situation and facing same problem...i'm able to get message.. but the supress property is not working.. is there any rivalry b/w messagebox & Suppresskey ??