is this CLICK EVENT working correctly?

I'm working on a VERY BASIC (no pun intended) VS2008.NET web page using Visual Basic.  User enters NETWORK DOMAIN and LOGON Id and clicks GET SID button.  Once SID is returned  A LOT of other goodies will happen, but i'm not there yet.
That CLICK_EVENT runs a FUNCTION that returns a TEXT string (SID or INVALID .... message).  If invalid, a boolean flag is set to false (done within function).
This is the BUTTON CLICK code.
        Dim txt As String

        txt = GetUserSID(TextBox1.Text, TextBox2.Text)

        TextBox3.Text = txt

        If SIDok = Then
            Button1.Enabled = False
            Button2.Enabled = True
 & ...