unhandled exception in crdb_adoplus.dll

Hi Friends,
I am using vs2002 and CR 9.1.In my application i have to Export the crystal report to PDF and i am able to do so using below code.

Code:

---


 Public Sub ExportToPDF()
            Dim rptDiskFileOptions As New DiskFileDestinationOptions()
            Try

                Dim FilePath As String

                FilePath = Server.MapPath(General.C_TempDownLoadPath & & "Report.pdf")
                '.Replace("/"c, "\")
                rptDiskFileOptions.DiskFileName = FilePath

                rptDoc = DirectCast(Cache(strCacheReport), ReportDocument)
                rptDoc.ExportOptions.ExportDestinationType = ExportDestinationType.DiskFile
                rptDoc.ExportOptions.DestinationOptions = rptDiskFileOptions
                rptDoc.ExportOptions.ExportFormatType = ExportFormatType.PortableDocFormat
                rptDoc.Export()

                Response.Redirect(General.C_TempDownLoadPath & "ReportName.pdf")

            Catch exc As Exception
                Throw exc
            Finally
                rptDoc = Nothing
                rptDiskFileOptions = Nothing
            End Try
        End Sub

---

Now my problem is that some time i am getting pdf file without any problem but most of the time it give me this exception.
An unhandled exception of type 'System.ExecutionEngineException' occurred in crdb_adoplus.dll

can anyone help me to resolved this problem.

Regards,
Ritesh

can anyone suggest me some solution :(