Export drawing to PDF using VB API

I am using VB API to connect to Creo Parametric 1.0 to extract data. I want to extract model drawing in PDF format and display it in my VB App.

When I call the Export method exception is thrown as : pfcExceptions::XToolkitInvalidType.

Does any one have any idea, what I should do?

Sub Main()

Dim asyncConnection As pfcls.IpfcAsyncConnection = Nothing 'conn

Dim cAC As pfcls.CCpfcAsyncConnection

Dim session As pfcls.IpfcBaseSession

Dim tModel As pfcls.IpfcModel

Try

cAC = New pfcls.CCpfcAsyncConnection 'asynconn

cAC = CreateObject("pfcls.pfcAsyncConnection")

asyncConnection = cAC.Connect("", "", "", 5)

session = asyncConnection.Session

Dim descModel As pfcls.IpfcModelDescriptor

Dim expdf As pfcls.IpfcPDFExportInstructions

Dim pdfopt As pfcls.IpfcPDFOption

Dim EpfcPDFOPT_LAUNCH_VIEWER As Boolean

EpfcPDFOPT_LAUNCH_VIEWER = False

descModel = (New pfcls.CCpfcModelDescriptor).Create(pfcls.EpfcModelType.EpfcMDL_DRAWING, "test.drw", Nothing)

expdf = (New pfcls.CCpfcPDFExportInstructions).Create()

pdfopt = (New pfcls.CCpfcPDFOption).Create()

pdfopt.OptionValue = (New pfcls.CMpfcArgument).CreateBoolArgValue(EpfcPDFOPT_LAUNCH_VIEWER)

expdf.FilePath = "c:\work\test.pdf"

tModel = session.CurrentModel

tModel.Export("c:\work\test.pdf", CType(expdf, pfcls.IpfcExportInstructions))

Catch ex As Exception

MsgBox(ex.Message.ToString + Chr(13) + ex.StackTrace.ToString)

Finally

asyncConnection.Disconnect(2)

End Try

End Sub