Consuming Web Service with SSL .p12 cert

Hello to all

I have a c# .net client that consumes a web service that uses a .p12 cert, but yesterday started to send a "Could not establish a trust relationship for the SSL/TLS secure channel" message, it had been working fine 2 years with the code:

                ServicePointManager.ServerCertificateValidationCallback = new System.Net.Security.RemoteCertificateValidationCallback(AcceptAllCertifications);

public bool AcceptAllCertifications(object sender, X509Certificate cert, X509Chain chain, SslPolicyErrors errors)
        {
            return true;
        } 

Has something change about accepting all kind of certs?

(Note: I have no problem consuming it with ApacheJmeter or Java client)

I apreciate your help