This is a common error. Unfortunately the causes are plenty. If it has never worked, it is likely a simple configuration problem.
In order for anyone to help you, you will likely need to supply more information, such as the scenario you have set up. Do you have a receive port and send port configured alone? If so, use a filter on your send port, such as: BTS.ReceivePortName == <Receive Port actual name goes here>.
Are you using an Orchestration that is connected using static ports, dynamic ports, request-response, one-way, etc? Have you tried simple projects to "black-box" test your problems? Also, make sure to clear out suspended messages and restart your Host Instance when you make changes to the app or re-deploy.
If none of this helps, please supply more information about your current application.