[DotNetDevelopment] How to get a node value or inner text from a xml string using xpath

[Pat 2345]

Heres my current code. How would I get the text of the element PNREF?
I want this value "AAA23459"

this line of code returns nothing to me.  Whats wrong with it.
 s = doc.SelectSingleNode("/http://www.Fin.com/ay/XMLResponse/
ResponseData/TransactionResults/TransactionResult/PNRef").InnerText




xmldata = "<XMLResponse xmlns=""http://www.Fin23.com/
ay""><ResponseData><Vendor>FIN</Vendor><Partner>FINl</
Partner><TransactionResults><TransactionResult><Result>54</
Result><IAVSResult>N</IAVSResult><AVSResult><StreetMatch>Match</
StreetMatch><ZipMatch>Match</ZipMatch></AVSResult><Message>Approved</
Message><PNRef>AAA23459</PNRef><AuthCode>2342</AuthCode></
TransactionResult></TransactionResults></ResponseData></XMLResponse>"

  Dim s As String
            'Load the XML so that we can parse it
            doc.LoadXml(xmldata)



            Root = doc.DocumentElement
   'I tried adding this but it didnt help
''Dim finMgr As New XmlNamespaceManager(doc.NameTable)
''finMgr.AddNamespace("fin", "http://www.Fin23.com/ay";)


            s = doc.SelectSingleNode("/http://www.Fin23.com/ay/
XMLResponse/ResponseData/TransactionResults/TransactionResult/
PNRef").InnerText