I was having the following exception when calling a wcf service from a Custom Workflow Activity: “When using System.ServiceModel.Channels.Message or types with MessageContractAttribute, the method must not use any other types of parameters.” And the reason was because when the svc service was added to the project, the configuration was:
After investigation, i discovered that the configuration should be with the check in Generate asynchronous operations instead. I will do more research and update with the reason that should be like this.