I did a Google search for the error "No operation description was found
for the service" and found this other SO posting.
web service using wsdl in Domino
The posting relates to a LotusScript Web Service, but the issue I
believe is the same. Both LotusScript and .Net are case insensitive
regarding their method/function declarations.
Reading the stack trace you're calling .helloWord(), could that you have
a name mismatch between your service and consumer ?