ปรึกษาปัญหาเกี่ยวกับ try exception ครับ ว่ามีหลักการเขียนอย่างไร

 strSQL = "SELECT COUNT(*) FROM article_tbl WHERE article_no = '" & articleNo & "'"
        objCmd = New OleDbCommand(strSQL, objConn)
        num = objCmd.ExecuteScalar()
        If num > 0 Then
            Response.Write("<script>alert('This article already existing,please check again');</script>")
            Response.Write("<script>window.location='add_art.aspx'</script>")
        Else
            Try
' ***first process

                strSQL = "INSERT INTO article_tbl (article_no,article_name,article_model,article_size, vender_id,maker,subcate_id,cate_id ,packing_unit,price,moq,leadtime,purchasing_by,certified_report,incoming_report,product_spec, fac_audit,date_modify,status,esd_control,show,art_comment,area)" & _
                " VALUES('" & articleNo & "','" & articleName & "','" & articleModel & "','" & articleSize & "', " & venderID & ",'" & selectMaker & "'," & subcategory_id & "," & category_id & ",'" & packingUnit & "','" & price2 & "','" & moq2 & "','" & leadTime & "', '" & purchasing2 & "','" & certified2 & "','" & incoming2 & "','" & specSheet & "','" & facAudit & "','" & dateTime & "'," & status & " ,'" & type & "',0,'" & comment.Text & "'," & select_area.Text & ")"
                objCmd = New OleDbCommand(strSQL, objConn)
                objCmd.ExecuteNonQuery()
            Catch ex As Exception
                '**** ตอนนี้ฟ้อง Error ที่ตรงนี้
                Response.Write("<script> alert('ERROR 001:" & ex.Message & "');</script>")
               '*** ฟ้อง Error เสร็จ ก็ให้ลิงค์ไปที่ชื่อไฟล์ add_art.aspx (ไฟล์เดิม เหมือนกับ รีเฟลชธรรมดา)
                Response.Write("<script>window.location='add_art.aspx';</script>")
            End Try

'***next process แต่พอมาดูผลมันจริงๆ ปรากฎว่า สคริปข้างล่างนี้ยังทำงานปกติ
            strSQL = "SELECT MAX(article_id) FROM article_tbl"
            objCmd = New OleDbCommand(strSQL, objConn)
            lastart = objCmd.ExecuteScalar()

            strSQL = "SELECT * FROM article_tbl WHERE article_id = " & lastart & ""
            objCmd = New OleDbCommand(strSQL, objConn)
            dtReader = objCmd.ExecuteReader()
            dtReader.Read()
            'File Upload 
            Dim objGraphic As System.Drawing.Image
            Dim objBitmap As Bitmap
            Dim intWidth As Integer = 100
            Dim intHeight As Integer = 0
            Dim bigWidth As Integer = 550
            Dim bigHeight As Integer = 0
            Dim i As Integer
            For i = 1 To 5
                Dim picture As FileUpload = FindControl("picture_" & i)
                Dim pictureName As String = dtReader.GetValue(1) & i & GetExtension(picture.FileName)
                If picture.HasFile Then
                    Try
                        strSQL = "INSERT INTO image_tbl (img_name,refarticle_id) VALUES ('" & pictureName & "'," & lastart & ")"
                        objCmd = New OleDbCommand(strSQL, objConn)
                        objCmd.ExecuteNonQuery()
                    Catch ex As Exception
                        Response.Write("<script> alert('ERROR 002:" & ex.Message & "');</script>")
                        Response.Write("<script>window.location='add_art.aspx'</script>")
                    End Try
                    picture.PostedFile.SaveAs(Server.MapPath("../tempPic/" & pictureName))
                    'Start Resize Big
                    objGraphic = System.Drawing.Image.FromFile(Server.MapPath("../tempPic/" & pictureName))
                    If bigHeight > 0 Then
                        objBitmap = New Bitmap(objGraphic, bigWidth, bigHeight)
                    Else
                        If objGraphic.Width > objGraphic.Height Then
                            If objGraphic.Width > bigWidth Then
                                Dim radio As Double = objGraphic.Height / objGraphic.Width
                                bigHeight = radio * bigWidth
                                objBitmap = New Bitmap(objGraphic, bigWidth, bigHeight)
                            Else
                                objBitmap = New Bitmap(objGraphic)
                            End If
                        Else
                            If objGraphic.Height > bigWidth Then
                                Dim radio As Double = objGraphic.Width / objGraphic.Height
                                bigHeight = radio * bigWidth
                                objBitmap = New Bitmap(objGraphic, bigHeight, bigWidth)
                            Else
                                objBitmap = New Bitmap(objGraphic)
                            End If
                        End If
                    End If
                    'Add ESD logo
                    If type = 1 Then
                        Dim picGraph As Graphics = Graphics.FromImage(objBitmap)
                        Dim overlay As Bitmap = New System.Drawing.Bitmap(Server.MapPath("../ESDlogo/ESDsign.gif"))
                        picGraph.DrawImage(overlay, (objBitmap.Width - (overlay.Width + 5)), 5)
                        overlay = Nothing
                        picGraph = Nothing
                    End If
                    objBitmap.Save(Server.MapPath("../BigPicture/" & pictureName))
                    objGraphic.Dispose()
                    objBitmap = Nothing
                    objGraphic = Nothing

                    'End Resize Big Pic
                    'Start Resize Thumpnail
                    objGraphic = System.Drawing.Image.FromFile(Server.MapPath("../BigPicture/" & pictureName))
                    ''---->crop picture
                    'Dim Lpoint As Integer = (objGraphic.Width / 2) - (objGraphic.Height / 2)
                    'Dim Rpoint As Integer = (objGraphic.Width / 2) + (objGraphic.Height / 2)
                    'objGraphic = CropImage(objGraphic, New Point(Lpoint, 0), New Point(Rpoint, objGraphic.Height))
                    ''---> end crop
                    If intHeight > 0 Then
                        objBitmap = New Bitmap(objGraphic, intWidth, intHeight)
                    Else
                        If objGraphic.Width > objGraphic.Height Then
                            If objGraphic.Width > intWidth Then
                                Dim radio As Double = objGraphic.Height / objGraphic.Width
                                intHeight = radio * intWidth
                                objBitmap = New Bitmap(objGraphic, intWidth, intHeight)
                            Else
                                objBitmap = New Bitmap(objGraphic)
                            End If
                        Else
                            If objGraphic.Height > intWidth Then
                                Dim radio As Double = objGraphic.Width / objGraphic.Height
                                intHeight = radio * intWidth
                                objBitmap = New Bitmap(objGraphic, intHeight, intWidth)
                            Else
                                objBitmap = New Bitmap(objGraphic)
                            End If
                        End If
                    End If
                    If type = 1 Then
                        Dim picGraph As Graphics = Graphics.FromImage(objBitmap)
                        Dim overlay As Bitmap = New System.Drawing.Bitmap(Server.MapPath("../ESDlogo/ESDsign_s.gif"))
                        picGraph.DrawImage(overlay, (objBitmap.Width - (overlay.Width + 5)), 5)
                        overlay = Nothing
                        picGraph = Nothing
                    End If
                    objBitmap.Save(Server.MapPath("../Thumpnail/" & pictureName))
                    objGraphic.Dispose()
                    objBitmap = Nothing
                    objGraphic = Nothing
                    Dim fileIn As New FileInfo(Server.MapPath("../tempPic/" & pictureName))
                    If fileIn.Exists Then
                        fileIn.Delete()
                    End If
                End If
            Next