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

Question

I am trying to consume a webservice and it is giving throwing this error.

Answer 1

When I've had errors like that they were due to either not having the service host name matching the one in the certificate it presents, or, less often, not having the appropriate certificate chain on the client to verify the server's certificate.

I would check the name you are contacting the service by and what the certificate it sends say -- you can watch the SSL negotiation with WireShark or similar, and see the strings in the second server packet.