adding certificate to SOAP web service.

Hello

I'm trying to call a webservice, which requires a certificate to work, the certeficate installed

on local machine in mmc.

i need to add a certificate using code to the web service instance.

NeqatyWSDL.NeqatyWSAPI neqatyWSAPI = new NeqatyWSDL.NeqatyWSAPI();
neqatyWSAPI.Url = "https://simb140.margento.com:48728";
X509Certificate2 cert = new X509Certificate2(@"D:\cert.p12","pass",X509KeyStorageFlags.DefaultKeySet);
neqatyWSAPI.ClientCertificates.Add(cert);
neqatyWSAPI.authorize(authorize);

The debugger stoped at the last line and raise error with the follwing:

The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.