.Net RC - Could not create the XML transformation....

I now have the IDP and SP samples that came with the .Net RC edition working - almost.

I can log in to the SP and when i select the "Click to Federate" link i am taken to the IDP Authenticator module at logonpost.aspx.
However, when i type in a username and password and click the submit button, i get the problem below. Anyone got any hints on I should do to fix this? 



Server Error in '/idp-sample' Application.
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Could not create the XML transformation identified by the URI http://www.w3.org/2001/10/xml-exc-c14n#. 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.Security.Cryptography.CryptographicException: Could not create the XML transformation identified by the URI http://www.w3.org/2001/10/xml-exc-c14n#.

Source Error: 


Line 134:                // Lastly, pass control back to SourceID, which will
Line 135:                // consequently pass control back to the SP.	
Line 136:                SourceID.HttpHandlers.Authenticator.Process(Context);
Line 137:            }
Line 138:            else
 

Source File: c:\inetpub\wwwroot\idp-sample\LogonPost.aspx.cs    Line: 136 

Stack Trace: 


[CryptographicException: Could not create the XML transformation identified by the URI http://www.w3.org/2001/10/xml-exc-c14n#.]
   System.Security.Cryptography.Xml.SignedXml.ComputeSignature()  1158
   SourceID.XmlUtils.SignResponse(ResponseAbstractType response, AsymmetricAlgorithm key, XmlSerializer serializer, Boolean isDebuggingEnabled) in C:\Documents and Settings\steven\My Documents\downloads\SourceID.NET-0.3\SourceID\XmlUtils.cs:324
   SourceID.HttpHandlers.Authenticator.HandleAuthReturnToSP(HttpContext context, AuthnRequestType authn_req, ProviderDirectory dir, SPDescriptorType sp) in C:\Documents and Settings\steven\My Documents\downloads\SourceID.NET-0.3\SourceID\HttpHandlers\Authenticator.cs:435
   SourceID.HttpHandlers.Authenticator.HandleAppAuthenticated(HttpContext context, AuthnRequestType authn_req, Object uid, ProviderDirectory dir, SPDescriptorType sp) in C:\Documents and Settings\steven\My Documents\downloads\SourceID.NET-0.3\SourceID\HttpHandlers\Authenticator.cs:242
   SourceID.HttpHandlers.Authenticator.Process(HttpContext context) in C:\Documents and Settings\steven\My Documents\downloads\SourceID.NET-0.3\SourceID\HttpHandlers\Authenticator.cs:86
   idp.LogonPost.Page_Load(Object sender, EventArgs e) in c:\inetpub\wwwroot\idp-sample\LogonPost.aspx.cs:136
   System.Web.UI.Control.OnLoad(EventArgs e)  67
   System.Web.UI.Control.LoadRecursive()  35
   System.Web.UI.Page.ProcessRequestMain()  720

 


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Version Information: Microsoft .NET Framework Version:1.1.4322.573; ASP.NET Version:1.1.4322.573