ไม่สามารถ delete file pdf ได้ ใช้ asp.net ( the process cannot access the file because it is being used by another process)

 If txtSubject.Text = String.Empty Then
            ScriptManager.RegisterStartupScript(Page, Page.GetType, "AlertMessage", "alert('Please enter Subject.');", True)
            txtSubject.Focus()
        ElseIf txtTo.Text = String.Empty Then
            ScriptManager.RegisterStartupScript(Page, Page.GetType, "AlertMessage", "alert('Please enter To.');", True)
            txtTo.Focus()
        ElseIf txtDetail.Text = String.Empty Then
            ScriptManager.RegisterStartupScript(Page, Page.GetType, "AlertMessage", "alert('Please enter Detail.');", True)
            txtDetail.Focus()
        ElseIf txtCC.Text = String.Empty Then
            ScriptManager.RegisterStartupScript(Page, Page.GetType, "AlertMessage", "alert('Please enter CC.');", True)
            txtCC.Focus()
        Else

            Try
                Dim rpts As CrystalDecisions.CrystalReports.Engine.ReportDocument = CType(Session("ReportDocument"), CrystalDecisions.CrystalReports.Engine.ReportDocument)
                Dim pathpdf As String = Server.MapPath(".") & "\PDFDownload\MogasAndKerosene_" & Session(USERNAME) & ".pdf"
                '  Dim pathpdf As String = Server.MapPath(".") & "\PDFDownload\MogasAndKerosene.pdf"

                Dim crExportOptions As ExportOptions
                Dim crDiskFileDestinationOptions As New DiskFileDestinationOptions()
                Dim crFormatTypeOptions As New PdfRtfWordFormatOptions()

                crDiskFileDestinationOptions.DiskFileName = pathpdf
                crFormatTypeOptions.FirstPageNumber = 1
                crFormatTypeOptions.LastPageNumber = 3
                crFormatTypeOptions.UsePageRange = True

                crExportOptions = rpts.ExportOptions
                With crExportOptions
                    .ExportDestinationType = ExportDestinationType.DiskFile
                    .ExportFormatType = ExportFormatType.PortableDocFormat

                    .ExportDestinationOptions = crDiskFileDestinationOptions
                    .ExportFormatOptions = crFormatTypeOptions
                End With
              
                Try
                    rpts.Export()
                    rpts.Close()
                    rpts.Dispose()
                    rpts = Nothing
                Catch ex As Exception

                End Try


                'Step SendMail
                Dim mail As New clsMail
                ' Dim mailSubject As String = "Mogas and Kerosene Update -" & txtDateNow.Text
                Dim mailForm As String = "<[email protected]>"
                '  Dim mailTo As String = "[email protected]"
                '  Dim mailCC As String = "[email protected]"
                Dim mailAtt As String = pathpdf
                Dim localPath As String = Server.MapPath("")
                Dim IsResult As Boolean = False
                '  IsResult = mail.SendMailFinish(localPath, mailForm, mailTo, mailCC, mailAtt, mailSubject)
                IsResult = mail.SendMailFinish(localPath, mailForm, mailAtt, txtSubject.Text, txtDetail.Text, txtTo.Text, txtCC.Text)
                If IsResult = True Then
                    ScriptManager.RegisterStartupScript(Page, Page.GetType, "AlertMessage", "alert('Send Email Successfull');", True)
                Else
                    ScriptManager.RegisterStartupScript(Page, Page.GetType, "AlertMessage", "alert('Send Email Unsuccess');", True)
                End If
               

            Catch ex As Exception

            End Try

            tdEdit.Visible = False
            txtSubject.Text = String.Empty
            txtDetail.Text = String.Empty
            txtCC.Text = String.Empty
            txtTo.Text = String.Empty

            'Dim FileEmail As New FileInfo(Server.MapPath(".") & "\PDFDownload\MogasAndKerosene_" & Session(USERNAME) & ".pdf")

            'If FileEmail.Exists Then
            '    FileEmail.Delete()
            'Else
            'End If
        


            Dim filePaths As String() = Directory.GetFiles(Server.MapPath(".") & "\PDFDownload\", "*.pdf")
            For Each filePath As String In filePaths
                File.Delete(filePath)
            Next
          
        End If