Export to pdf error

My Crystal report use store procedure as data source. Code1 is works. Once I add code2 to export to pdf, an error occured.
How to fix it?

//code1 works fine and displays report on screen.

Dim crd As New ReportDocument
crd.Load(Server.MapPath("myCrystalReport.rpt"))
crd.SetDatabaseLogon("myID", "Password", "ServerName", "DBName")
CrystalReportViewer1.ReportSource = crd

//code2 do not work said that "Missing parameter values" at " crystalReportViewer1.FormatEngine.ExportToStream(req)"

Dim exp As New ExportOptions()
exp.ExportFormatType = ExportFormatType.PortableDocFormat
exp.FormatOptions = New PdfRtfWordFormatOptions()
Dim req As New ExportRequestContext()
req.ExportInfo = exp
Dim st As System.IO.Stream
st = crystalReportViewer1.FormatEngine.ExportToStream(req) //Missing parameter values
Response.ClearHeaders()
Response.ClearContent()
Response.ContentType = "application/pdf"
Dim b(st.Length - 1) As Byte
st.Read(b, 0, CInt(Fix(st.Length)))
Response.BinaryWrite(b)