Probleme sauvegarde xls dans vb .net

Imports Microsoft.Office.Interop.Excel
Public Class Form1




Dim app = CreateObject("excel.application")
    Dim workbook = app.workbooks.Open("c:\ilwcentral\tot.xlsx")
    Dim WorkSheet = app.ActiveWorkbook.ActiveSheet
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click




Using MyReader As New Microsoft.VisualBasic.
                       FileIO.TextFieldParser(
                         "C:\ilwcentral\mag1.txt")
            MyReader.TextFieldType = FileIO.FieldType.Delimited
            MyReader.SetDelimiters(";")
            Dim currentRow As String()
            While Not MyReader.EndOfData
                Dim i = 1
                Dim j = 2
                Try
                    currentRow = MyReader.ReadFields

Dim currentField As String
                    j = j + 1

For Each currentField In currentRow

If i = 1 Then

WorkSheet.Cells(1, 1).Value = "toto"
                        End If
                        If i = 2 Then
                            WorkSheet.Cells(j, 2).Value = currentField
                        End If
                        If i = 3 Then
                            WorkSheet.Cells(j, 3).Value = currentField
                        End If
                        If i = 4 Then
                            WorkSheet.Cells(j, 4).Value = currentField
                        End If
                        If i = 5 Then
                            WorkSheet.Cells(j, 5).Value = currentField
                        End If
                        If i = 6 Then
                            i = 0
                        End If


i = i + 1
                    Next
                Catch ex As Microsoft.VisualBasic.
                            FileIO.MalformedLineException
                    MsgBox("Line " & ex.Message &
                    "is not valid and will be skipped.")
                End Try
            End While
            workbook.Save()
        End Using



End Sub

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load




End Sub
    Private Sub Form1_FormClosed(ByVal sender As System.Object, _
 ByVal e As System.Windows.Forms.FormClosedEventArgs) _
  Handles MyBase.FormClosed



workbook.Close(True)
        app.Quit()
    End Sub

End Class

EDIT : Ajout des balises de code

EDIT² : Sujet déplacé dans le forum : VB