Correlation Services prevent Model Execution

I am trying to get my head around Correlation Services in order to migrate some RosettaNet conversation scripts to Modeler 6.1.5.
In order to ensure that acks get put to the correct instanceID I believe I need a correlationID to be generated when the initial instance is triggered by the arrival of an external document from TN and then when any other step in the Model is waiting on additional external or back end docs (i.e. acks)

In modeler i built a test flow which subscribes to a TN document.
I associate a Correlation Service to that start step and put in a 2nd Flow step just to do some output debug, I am just trying to see how the correlation service gets called.

I created a service with the specification from the Modeler users guide
and I set the property of correlation service on the start step (which does the tn.view) to be my correlation service (which is returning a fixed string right now). Now if I submit a trigger document to that server the model does not run and I get XML Document was not submitted.

I am trying to figure out how the correlation service is called and where I can pick up the return information (ProcessCorrelationID) from .
Right now it does not appear that the correlation service is started at all.