Error while sending fax using ASP.net and FAXCOMEXLib as COMException (0x800710D8): Operation failed

I have asp.net application to send FAX using FAXServer using FAXCOMEXLib.dll

I am getting COMException (0x800710D8): Operation failed. I know one workaround to set application pool identity. but which user i have to set as application identity that don't know.

For windows application with same code,I am not getting any error and fax sent successfully for ASP.NET application, fax without attachment sent successfully, but if I attach file .pdf,.html,.jpg,.tif , exception is coming.

Q. why windows application works?

FAXserver has network domain is 'THEPRO" and Users are "FAXPRO\Admin" and "FAXPRo\Users" Application pool details is "Network service", 4.0 framework and Integrated mode. Window user id 'THEPRO\IDSAdmin'.

*Q.Please let me know which user account I have to set as application pool identity? Q. Is there any other workaround?*

Code is as below

  int JobID = 0;
        FAXCOMEXLib.FaxServer faxsrv = new FAXCOMEXLib.FaxServerClass();
        FAXCOMEXLib.FaxDocument faxdoc = new FAXCOMEXLib.FaxDocument();
        FAXCOMEXLib.FaxSender oSender;



            object Job;
            string FilePath="";
            faxsrv.Connect(faxServer);
            oSender = faxdoc.Sender;

            faxdoc = new FAXCOMEXLib.FaxDocumentClass();


            //Name the document
            oSender.LoadDefaultSender();
            faxdoc.Sender.Email = oSender.Email;
            faxdoc.Sender.Company = oSender.Company;
            faxdoc.Sender.City = oSender.City;
            faxdoc.Sender.FaxNumber = oSender.FaxNumber;
            faxdoc.Sender.OfficePhone = oSender.OfficePhone;
            faxdoc.Sender.Title = oSender.Title;
            faxdoc.DocumentName = "ProCare";

            if (!string.IsNullOrEmpty(faxCoverPage))
            {

                faxdoc.CoverPageType = FAXCOMEXLib.FAX_COVERPAGE_TYPE_ENUM.fcptSERVER;
                faxdoc.CoverPage = faxCoverPage;//"ProCare";//"C:\\URGENT.COV";
            }            

            faxdoc.Subject = subject;
            faxdoc.Recipients.Add(faxnumber, recipientName);


            if (!string.IsNullOrEmpty(attachmentFile))
            {
                faxdoc.Body = @attachmentFile;

            }


            Job = faxdoc.ConnectedSubmit(faxsrv);

My first try: Open up task manager... check under which context w3wp.exe is executing and give that user access.