ช่วยหนูที มีปัญหาเรื่องการ Insert ข้อมูลลงตาราง ค่ะ

code ที่ได้เขียนไวในตอนแรก 

Protected Sub btnrecord_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnrecord.Click
        Dim strConn As String
        strConn = WebConfigurationManager.ConnectionStrings("CPETC").ConnectionString
        '======================================
        Dim Con As New SqlConnection(strConn)
        Con.Open()

        Dim conn As New SqlConnection(strConn)
        Dim sql As String = "SELECT dbo.Semaster.Semasterid, dbo.Regis_learn.subjectid, dbo.Regis_learn.Username, dbo.Profiles.Firstname, dbo.Profiles.Lastname FROM dbo.Semaster INNER JOIN dbo.Regis_learn ON dbo.Semaster.Semasterid = dbo.Regis_learn.semasterid INNER JOIN dbo.Profiles ON dbo.Regis_learn.Username = dbo.Profiles.Username WHERE (subjectid = '" & Request.QueryString("subjectid") & "') "
        Dim adapter As SqlDataAdapter
        adapter = New SqlDataAdapter(sql, conn)
        Dim ds As New DataSet()
        adapter.Fill(ds, "test")
        Dim MaxRow As Integer = ds.Tables("test").Rows.Count
        Dim i As Integer
        Dim ds1 As New DataSet()

        For i = 0 To MaxRow - 1

            Dim Username As String
            Dim Semasterid As String
            Dim Subjectid As String
            Dim Grade As String

            Username = ds.Tables(0).Rows(i)(2).ToString()
            Semasterid = ds.Tables(0).Rows(i)("semasterid").ToString()
            Subjectid = ds.Tables(0).Rows(i)("subjectid").ToString()
            Grade = Request("Select1" + i.ToString)

            Dim sqlsub As String = " SELECT     dbo.Semaster.Semasterid, dbo.Regis_grade.subjectid, dbo.Regis_grade.username, dbo.Profiles.Firstname, dbo.Profiles.Lastname"
            sqlsub = sqlsub + "  FROM         dbo.Semaster INNER JOIN"
            sqlsub = sqlsub + "          dbo.Regis_grade ON dbo.Semaster.Semasterid = dbo.Regis_grade.semasterid INNER JOIN"
            sqlsub = sqlsub + "          dbo.Profiles ON dbo.Regis_grade.username = dbo.Profiles.Username WHERE subjectid = '" & Request.QueryString("subjectid") & "' AND  dbo.Regis_grade.username='" & Username & "'"

            Dim adapter1 As SqlDataAdapter
            adapter1 = New SqlDataAdapter(sqlsub, conn)
            adapter1.Fill(ds1, "test")
            Dim iMax As Integer = ds1.Tables("test").Rows.Count

            If iMax = 0 Then

                'Dim Firstname As String 
                'Dim Lastname As String

                addgrade(Semasterid, Subjectid, Username, Grade)
                Label1.Text = "บันทึกผลการเรียนเรียบร้อย"
                Label1.ForeColor = Drawing.Color.Red
                Con.Close()
            End If
        Next
    End Sub