I Attached programmatically a client certificate to a Web Service Proxy like
Microsoft Exemple
// Create a new instance of a proxy class for the Bank XML Web service.
BankSession bank = new BankSession();

// Load the client certificate from a file.
X509Certificate x509 = X509Certificate.CreateFromCertFile(@"c:\user.cer");

// Add the client certificate to the ClientCertificates property of the
proxy class.
bank.ClientCertificates.Add(x509);

// Communicate with the Deposit XML Web service method,
// which requires authentication using client certificates.
bank.Deposit(500);

When try to retrieve the certificate on Web Service side:

HttpClientCertificate cs = Context.Request.ClientCertificate;

byte[] rawcert = cs.Certificate;

No certificate is passed.

Wehen I try to call the Web Service withe the I.E. Bowser and supplying a
client certificate, it woorkd fine! What I'm doing wrong?

Thanks for your help