มีปัญหาการ Insert ข้อมูลลง Sql แล้วข้อมูลเบิ้ลเป็นสองชุดเป็นบางครั้ง

 Protected Sub btnSubmit_click(ByVal sender As Object, ByVal e As EventArgs)

        Dim empid As String = Session("Emp")

        Dim ip As String = HttpContext.Current.Request.ServerVariables("REMOTE_ADDR")
        'lblID.Text = ip
        Dim clientMachineName As String
        clientMachineName = (Dns.GetHostEntry(Request.ServerVariables("remote_addr")).HostName)
        For Each item As RepeaterItem In RepterDetails.Items

            Dim Chkbox As CheckBox = TryCast(item.FindControl("CheckBox1"), CheckBox)

            Dim lblProduct As Label = CType(item.FindControl("lblComment"), Label)
            Dim product As String = lblProduct.Text

            Dim subgroup As Label = CType(item.FindControl("Label1"), Label)
            Dim subgroup_id As String = subgroup.Text

            Dim FooterTemplate As Control = RepterDetails.Controls(RepterDetails.Controls.Count - 1).Controls(0)
            Dim lblFooter As CheckBox = TryCast(FooterTemplate.FindControl("CheckBox2"), CheckBox)

            If lblFooter IsNot Nothing AndAlso lblFooter.Checked Then
                Response.Write(Chkbox.Text)
                con.Open()
                cmd = New SqlCommand("insert into Vote_CMT (Employee_ID,Group_ID,SubGroup_ID,IP_Address,Name_pc,Candidate_ID) values(@Employee_ID,@group_id,@subgroup_id,@ip,@pc_name,'0')", con)

                cmd.Parameters.Clear()
                cmd.Parameters.Add("@Employee_ID", SqlDbType.VarChar).Value = empid.ToString()
                cmd.Parameters.Add("@candidate_id", SqlDbType.VarChar).Value = Chkbox.Text.ToString()
                cmd.Parameters.Add("@group_id", SqlDbType.VarChar).Value = lblProduct.Text.ToString()
                cmd.Parameters.Add("@subgroup_id", SqlDbType.VarChar).Value = subgroup.Text.ToString()
                cmd.Parameters.Add("@ip", SqlDbType.VarChar).Value = ip
                cmd.Parameters.Add("@pc_name", SqlDbType.VarChar).Value = clientMachineName
                cmd.ExecuteNonQuery()

                con.Close()

                Exit For

            ElseIf Chkbox IsNot Nothing AndAlso Chkbox.Checked Then

                Response.Write(Chkbox.Text)
                con.Open()
                cmd = New SqlCommand("insert into Vote_CMT (Employee_ID,Group_ID,SubGroup_ID,IP_Address,Name_pc,Candidate_ID) values('" & empid & "',@group_id,@subgroup_id,@ip,@pc_name,@candidate_id)", con)

                cmd.Parameters.Clear()

                cmd.Parameters.Add("@candidate_id", SqlDbType.VarChar).Value = Chkbox.Text.ToString()
                cmd.Parameters.Add("@group_id", SqlDbType.VarChar).Value = lblProduct.Text.ToString()
                cmd.Parameters.Add("@subgroup_id", SqlDbType.VarChar).Value = subgroup.Text.ToString()
                cmd.Parameters.Add("@ip", SqlDbType.VarChar).Value = ip
                cmd.Parameters.Add("@pc_name", SqlDbType.VarChar).Value = clientMachineName
                cmd.ExecuteNonQuery()

                con.Close()

            End If


        Next

        Updateuser_vote((Session("Emp")))
        Response.Redirect("success.aspx")

        'Server.Transfer("success.aspx", False)
        'BindRepeater()

    End Sub