Debug a Small Desktop Program -- 2

I have a working small desktop program that securely contacts a web service sending it requests and getting back responses. Written in VB.NET, uses security certificates, SOAP envelopes, wsdl. The server recently upgraded its security certificate from SHA1 to SHA256 (SHA2). It took my programmer an hour to upgrade our client application to use the new security certificate and then he left town. The upgraded application is working successfully on some transaction but giving an error on others, and I don't understand security. Can somebody help? I can have you connect remotely to show you both almost-identical-programs in debug mode. One is working for all cases (using SHA1) and the other (SHA256) gives an error on certain transactions. See attached text file for error message and specs.