VB.Net save excel file only in program debugging - asp.net

Question

I got a problem which is not an error in writing data to Excel file from VB.NET.
The code to save data in Excel file is as the following:
Sub WriteToExcel(ByVal dt As DataTable)
Dim excel_app As New Excel.ApplicationClass()
excel_app.Visible = True
Dim workbook As Excel.Workbook = excel_app.Workbooks.Open(Filename:=FileUpload1.PostedFile.FileName)
Dim sheet_name As String = "rptSyncADandITSM"
Dim sheet As Excel.Worksheet = FindSheet(workbook, sheet_name)
sheet.Cells(1, "AF") = "Status"
sheet.Cells(1, "AG") = "Message"
sheet.Range("AF" & 1).Style.VerticalAlignment = VerticalAlign.Top
sheet.Range("AF1").Style.HorizontalAlignment = HorizontalAlign.Center
sheet.Range("AF1").ColumnWidth = 10
sheet.Range("AG1").Style.VerticalAlignment = VerticalAlign.Top
sheet.Range("AG1").Style.HorizontalAlignment = HorizontalAlign.Center
sheet.Range("AG1").ColumnWidth = 15
Dim header_range As Excel.Range = sheet.Range("AF1", "AG1")
header_range.Font.Bold = True
header_range.Font.Color = System.Drawing.ColorTranslator.ToOle(Drawing.Color.Black)
Dim borders As Excel.Borders = header_range.Borders
borders.LineStyle = Excel.XlLineStyle.xlContinuous
borders.Weight = 1.9R
For Each dr As DataRow In dt.Rows
Dim value_range As Excel.Range = sheet.Range("AF" & dr(0).ToString, "AG" & dr(0).ToString)
If Not dr.IsNull(0) Then
sheet.Range("AF" & dr(0).ToString).Style.VerticalAlignment = VerticalAlign.Top
sheet.Range("AF" & dr(0).ToString).Style.HorizontalAlignment = HorizontalAlign.Center
sheet.Range("AF" & dr(0).ToString).ColumnWidth = 10
sheet.Range("AG" & dr(0).ToString).Style.VerticalAlignment = VerticalAlign.Top
sheet.Range("AG" & dr(0).ToString).Style.HorizontalAlignment = HorizontalAlign.Center
sheet.Range("AG" & dr(0).ToString).ColumnWidth = 15
Dim values(0, 1) As String
values(0, 0) = dr(1).ToString
values(0, 1) = dr(2).ToString
value_range.Value2 = values
End If
Dim value_borders As Excel.Borders = value_range.Borders
value_borders.LineStyle = Excel.XlLineStyle.xlContinuous
value_borders.Weight = 2.0R
Next
workbook.Save()
workbook.Close()
'workbook.Close(SaveChanges:=True)
excel_app.Quit()
End Sub
I reference these codes from this
But it only works when i debug the program. In runtime(not debugging) doesn't work to save.