ติดปัญหาเรื่องการ login ชื่อซ้ำกันได้ค่ะ asp.net by vb.net ใช้วิธีการเก็บค่าไว้ใน session ค่ะ

<input  type="checkbox" name="cbxClearSession" id="cbxClearSession"  value="Clear" runat="server" visible="false" /><span id="sp_session" runat="server"></span>

Protected Sub Loginbtn_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Loginbtn.Click

if me.cbxClearSession.checked = true and Session("strUser") <> "" then
Session("strUser") = Nothing
Session("Authen") = Nothing
end if

if Me.Usertxt.Text <> "" and Me.Passtxt.Text <> "" and Session("strUser") <> "" then
   if lcase(Me.Usertxt.Text) = lcase(Session("strUser")) then
      Me.lblstatus.Visible = True
      Me.lblstatus.Text = "User ¹ÕéÁÕ¡Òà login ÍÂÙèáÅéÇã¹¢³Ð¹Õé"
      me.cbxClearSession.Visible = True
      me.sp_session.innerHTML = "µéͧ¡Òà clear session ËÃ×ÍäÁè ?"
      response.end
   end if
end if

strcon = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\DbRegister.accdb"
con.ConnectionString = strcon
con.Open()
Dim intNumRows As Integer
Dim atl As String
strsql = "SELECT COUNT(*)FROM DbLogin WHERE Username = '" & Me.Usertxt.Text & "' AND PasswordLogin = '" & Me.Passtxt.Text & "' "
cmd = New OleDbCommand(strsql, con)
intNumRows = cmd.ExecuteScalar()


If intNumRows <= 0 Then
Me.lblstatus.Visible = True
Me.lblstatus.Text = "ª×èÍ username ËÃ×Í password äÁè¶Ù¡µéͧ ¡ÃسҵÃǨÊͺÍÕ¡¤ÃÑé§"

Else

Dim sql As String
sql = "SELECT Access FROM DbLogin WHERE Username = '" & Me.Usertxt.Text & "' "
Dim cmd1 As OleDbCommand
cmd1 = New OleDbCommand(sql, con)

readstrsql = cmd1.ExecuteReader



readstrsql.Read()

atl = readstrsql("Access")
If intNumRows > 0 Then
Session("strUser") = Me.Usertxt.Text
Session("Authen") = atl
Response.Redirect("MenuRegister.aspx")

Else


Me.lblstatus.Visible = True

Me.lblstatus.Text = "Username/Password is wrong."

End If


End If



con.Close()

con = Nothing
End Sub

		Dim intNumRows As Integer
		strSQL = "SELECT COUNT(*) FROM member WHERE Username = '"& Me.txtUsername.Text &"' AND [Password] = '"& Me.txtPassword.Text &"' "		
		objCmd = New OleDbCommand(strSQL, objConn)
		intNumRows = objCmd.ExecuteScalar()

		IF intNumRows > 0 Then
			Session("strUser") = Me.txtUsername.Text
			Response.Redirect("Page1.aspx")
		Else	
			Me.pnlLogin.Visible = False
			Me.lblStatus.Visible = True
			Me.lblStatus.Text = "Username/Password is wrong."
		End IF

  'Function เช็ค status login
    Private Function CheckLoginByUser() As Boolean

        Call connectionDB()
        sb.Remove(0, sb.Length)
        sb.Append(" select * from Login ")
        sb.Append(" where status ='1' ")
        sb.Append(" and username ='admin' ")
        da = New OleDbDataAdapter(sb.ToString(), con)
        If Not ds.Tables("dtLogin") Is Nothing Then
            ds.Tables("dtLogin").Clear()
        End If
        da.Fill(ds, "dtLogin")

        If ds.Tables("dtLogin").Rows(0).Item("status").ToString() = "1" Then
            Return False
        End If

        Return True
    End Function

'เรียกใช้งาน Function
    Private Sub Login()
        If (CheckLoginByUser() = False) Then
            MsgBox("มีการใช้งาน ผ่าน UserName  นี้แล้ว กรุณาตรวจสอบใหม่อีกครั้ง ", MsgBoxStyle.Critical, "ผลการตรวจสอบ")
            Exit Sub
        End If
    End Sub