I'm sorry, but this is a weird question...
Why is the first request to a WebService returning "Could not establish trust relationship for SSL/TLS secure channel", and the next requests (all of them) are running ok?
I launch the request from my client application by clicking on a button. Then, the request is built with the proper values of address, binding and contract. The first click always returns the exception. Without closing the application, the next clicks launch the request properly.
Please don't close this question for being "unconstructive".
Regards