сохранить файл Excel с epPlus

Question

У меня проблема при сохранении файла Excel в приложении UWP (шаблон Windows):

        Dim excel As ExcelPackage = New ExcelPackage()

        excel.Workbook.Worksheets.Add("Worksheet 1")
        excel.Workbook.Worksheets.Add("Worksheet 2")
        excel.Workbook.Worksheets.Add("Worksheet 3")

        Dim excelFile As FileInfo = New FileInfo("test2.xlsx")

        OutputTextBlock.Text = excelFile.ToString()

        excel.SaveAs(excelFile)

        Process.Start(excelFile.ToString())

Ошибки

'System.UnauthorizedAccessException' в System.Private.CoreLib.dll

'System.InvalidOperationException' в EPPlus.dll

Как ее решить?

---

ОБНОВЛЕНИЕ

Пример пути, который работает при сохранении с использованием FileSavePicker:

        OutputTextBlock.Text = ""
        Dim savePicker As FileSavePicker = New FileSavePicker()
        savePicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary
        savePicker.FileTypeChoices.Add("Plain Text", New List(Of String)() From {
            ".txt"
        })
        savePicker.SuggestedFileName = "New Document"
        Dim file As StorageFile = Await savePicker.PickSaveFileAsync()

        If file IsNot Nothing Then
            CachedFileManager.DeferUpdates(file)
            Await FileIO.WriteTextAsync(file, "Example file contents.")
            Dim status As FileUpdateStatus = Await CachedFileManager.CompleteUpdatesAsync(file)

            If status = FileUpdateStatus.Complete Then
                OutputTextBlock.Text = "File " & file.Name & " was saved."
            ElseIf status = FileUpdateStatus.CompleteAndRenamed Then
                OutputTextBlock.Text = "File " & file.Name & " was renamed and saved."
            Else
                OutputTextBlock.Text = "File " & file.Name & " couldn't be saved."
            End If
        Else
            OutputTextBlock.Text = "Operation cancelled."
        End If