Issue on Crystal report exporting to PDF format- Database logon failed

string sPDFReportFile = "Payslip-" + _common.Utility.ToString(cmbMonth.Items[cmbMonth.SelectedIndex].Value) + Utility.ToString(cmbYear.Items[cmbYear.SelectedIndex].Value) + "-" + _common.Utility.ToString(Session.SessionID) + "." + Utility.ToString(filetype).Trim();
CrystalDecisions.Shared.DiskFileDestinationOptions dfdoReport = new CrystalDecisions.Shared.DiskFileDestinationOptions();
dfdoReport.DiskFileName = Request.PhysicalApplicationPath + @"TempReports\" + sPDFReportFile;
ReportDoc.ExportOptions.ExportDestinationType = CrystalDecisions.Shared.ExportDestinationType.DiskFile;
if (filetype == "doc")
    ReportDoc.ExportOptions.ExportFormatType = CrystalDecisions.Shared.ExportFormatType.RichText;
else if (filetype == "pdf")
    ReportDoc.ExportOptions.ExportFormatType = CrystalDecisions.Shared.ExportFormatType.PortableDocFormat;

ReportDoc.ExportOptions.DestinationOptions = dfdoReport;
ReportDoc.Export();
ReportDoc.Close();
ReportDoc.Dispose();

return Utility.ToString(sPDFReportFile);