Message signing in wcf using x509 certificate

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C#

ASP.NET

WCF

security

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I am facing an issue while trying to consume a WCF web service which requires mutual authentication and message signing using X509 certificate. I have already implemented mutual authentication using X509 certificate, but I am facing an issue while trying to implement message signing. I have successfully installed certificates on my machine. The error message I am getting is:
Signature verification failed
Please note I have successfully tested this application using SoapUI. But I am facing this issue while trying to implement the same in C#.
Below is the code i am using for achieving the same:

public override void SecureMessage(SoapEnvelope envelope, Security security)
       {
           // Get an X.509 certificate for signing the SOAP message.
           X509SecurityToken signatureToken = GetSecurityToken("subjectname");
           if (signatureToken == null)
           {
               throw new SecurityFault("Message Requirements could not be satisfied.");
           }

           // Add the X.509 certificate to the header.
           security.Tokens.Add(signatureToken);

           // Specify that the SOAP message is signed using this X.509
           // certifcate.
           MessageSignature sig = new MessageSignature(signatureToken);
           security.Elements.Add(sig);
       }

       public X509SecurityToken GetSecurityToken(string subjectName)
       {
           X509SecurityToken objX509SecurityToken = null;
           X509Store objX509Store = new X509Store(StoreName.My, StoreLocation.CurrentUser);
           objX509Store.Open(OpenFlags.ReadOnly);
           try
           {
               X509Certificate2Collection objX509Certificate2Collection = objX509Store.Certificates.Find(X509FindType.FindBySubjectName, subjectName, true);

               X509Certificate2 objX509Certificate2;
               if (objX509Certificate2Collection.Count == 1)
               {
                   objX509Certificate2 = objX509Certificate2Collection[0];
                   objX509SecurityToken = new X509SecurityToken(objX509Certificate2);
               }
               else
               {
                   objX509SecurityToken = null;
               }
           }
           catch (Exception ex)
           {
               objX509SecurityToken = null;
           }
           finally
           {
               if (objX509Store != null)
                   objX509Store.Close();
           }
           return objX509SecurityToken;
       }

[edit] phil.o - Code block added for readibility purpose [/edit]