Problem automating PDFCreator in VFP 5

I'm having a problem automating PDFCreator in Visual FoxPro 5.  It always gives an error whenever I try to set any values for the options (for example on the last 3 lines of this code)

LOCAL oPdf as Object
oPdf= CREATEOBJECT("PDFCreator.clsPDFCreator")
oPdf.cVisible = .T.
oPdf.cPrinterStop = .F.
oPdf.cOption("AutosaveDirectory") = pc_pdfdir
oPdf.cOption("AutosaveFilename")= pc_pdffn
oPdf.cOption("UseAutosave")= 1

The error message I get says "Function argument type or count is invalid".

Any ideas what I'm doing wrong?