Problem in SaveAs method on VSTO Word Add-in

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VB9

C#

VB

private void SaveAs(string strFileName, Word.Document d)
        {
            object missing = System.Reflection.Missing.Value;
            object fileName = strFileName;
            object format = Word.WdSaveFormat.wdFormatDocumentDefault;
            d.SaveAs(ref fileName, ref format, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing);
        }

I have added save button on my ribbon. When I'm going to save the active document the error was "Command Failed".

Please help. Thanks!