WCF Web Service with Biztalk Receive Location and Receive ****t

Hi ,
I configured the binding on the Receive Location (with the Biztalk Admin 
tool): WS_HTTP with message security using a certificate. I installed a
demo 
CA Authority and a demo certificate, following 
http://msdn.microsoft.com/en-us/library/bb259973.aspx
and 
http://msdn.microsoft.com/en-us/library/bb226411.aspx
 . I gave access to 
the certificate private key to almost all the users on my machine
(including 
btssvc, ASPNET and NETWORK SERVICE) and I still have this error when I
call 
the Web Service from a client application (the message is translated from 
French but it must be very near from the exact English message):

Event type :  Error
Event Source :              System.ServiceModel 3.0.0.0
Event Category :         WebHost
Event ID :        3
Date :                    5/29/2008
Time :                 4:45:40 PM
User :         VM-BTS06R2-DEV\btssvc
Computer :       VM-BTS06R2-DEV
Description :
WebHost failed to process a request.
 Sender Information: 
System.ServiceModel.ServiceHostingEnvironment+HostingManager/32347029
 Exception: System.ServiceModel.ServiceActivationException: The service « 
/EnvoiDCI/WcfService_EnvoiDCIOrchestrastion.svc » cannot be activated 
because of a compilation exception. The exception message is : Impossible
to 
find the X.509 certificate with the following search criteria : StoreName 
« My », StoreLocation « CurrentUser », FindType « FindByThumbprint », 
FindValue « 427407008D306CB047E2CC8B819FBCB1CFDE136B ».. ---> 
System.InvalidOperationException: Impossible to find the X.509 certificate

with the following search criteria : StoreName « My », StoreLocation « 
CurrentUser », FindType « FindByThumbprint », FindValue « 
427407008D306CB047E2CC8B819FBCB1CFDE136B ».
   at 
System.ServiceModel.Security.SecurityUtils.GetCertificateFromStoreCore(StoreName

storeName, StoreLocation storeLocation, X509FindType findType, Object 
findValue, EndpointAddress target, Boolean throwIfMultipleOrNoMatch)
   at 
System.ServiceModel.Security.SecurityUtils.GetCertificateFromStore(StoreName

storeName, StoreLocation storeLocation, X509FindType findType, Object 
findValue, EndpointAddress target)
   at 
System.ServiceModel.Security.X509CertificateRecipientServiceCredential.SetCertificate(StoreLocation

storeLocation, StoreName storeName, X509FindType findType, Object
findValue)
   at 
Microsoft.BizTalk.Adapter.Wcf.Runtime.BtsServiceHostBase.SetServiceCertificate()
   at 
Microsoft.BizTalk.Adapter.Wcf.Runtime.BtsServiceHostBase.InitializeRuntime()
   at 
Microsoft.BizTalk.Adapter.Wcf.Runtime.WebServiceHost`3.InitializeRuntime()
   at System.ServiceModel.ServiceHostBase.OnOpen(TimeSpan timeout)
   at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan 
timeout)
   at System.ServiceModel.Channels.CommunicationObject.Open()
   at 
System.ServiceModel.ServiceHostingEnvironment.HostingManager.ActivateService(String

normalizedVirtualPath)
   at 
System.ServiceModel.ServiceHostingEnvironment.HostingManager.EnsureServiceAvailable(String

normalizedVirtualPath)
   --- End of the Internal exception stack ---
   at 
System.ServiceModel.ServiceHostingEnvironment.HostingManager.EnsureServiceAvailable(String

normalizedVirtualPath)
   at 
System.ServiceModel.ServiceHostingEnvironment.EnsureServiceAvailableFast(String

relativeVirtualPath)
 Process Name: w3wp
 Process ID: 1244

Does anyone have an idea? Thank you

Marc