SignedXML.Check Signature() not working

[ChrisA]

I'm using Michael Gallants DecodeCertKey example to get the public key
from an X509 certificate. I then create an RSAServiceProvi der and try
to use it to CheckSignature( ) on the signed XML file. Other sources
such as http://www.infomosaic.net/XMLSign/SecureXMLVerifyWS.htm can
verify the signature, but .Net won't. Any ideas?

Here is the code I'm using:

' Verify the signature of an XML file and return the result.
Public Shared Function VerifyXmlFile(B yVal Name As String) As
Boolean

' Create a new XML document.
Dim xmlDocument As New XmlDocument

' Format using white spaces.
xmlDocument.Pre serveWhitespace = True

' Load the passed XML file into the document.
xmlDocument.Loa d(Name)

Dim oRSA As RSACryptoServic eProvider
' Load the X509 certificate.
Dim x509Cert As X509Certificate =
X509Certificate .CreateFromCert File("mycert.ce r")

'//Create a new instance of RSACryptoServic eProvider.
oRSA = DecodeCertKey.D ecodeObject(x50 9Cert.GetPublic Key())

' Create a new SignedXml object and pass it
' the XML document class.
Dim signedXml As New SignedXml

' Find the "Signature" node and create a new
' XmlNodeList object.
Dim nodeList As XmlNodeList =
xmlDocument.Get ElementsByTagNa me("ds:Signatur e")

' Load the signature node.
signedXml.LoadX ml(CType(nodeLi st(0), XmlElement))

' Check the signature and return the result.
Return signedXml.Check Signature(oRSA)

End Function