Vista - WCF giving an error that I don't understand.

When I try to view the .svc file in a browser I get:

The operation 'GetBsiServicesDataMessage' could not be loaded because it has
a parameter or return type of type System.ServiceModel.Channels.Message or a
type that has MessageContractAttribute and other parameters of different
types. When using System.ServiceModel.Channels.Message or types with
MessageContractAttribute, the method must not use any other types of
parameters.

I am not sure what I am doing wrong. Any ideas?

Thank you.

Kevin