vCAC Design Center - Error creating a custom workflow

I've set up a very small vCAC lab environment and am trying to play with custom workflows in the vCAC designer.  I've installed the client, launched it, and clicked load.  I select WFStubBuildingMachine, double click on building machine, then custom code.  I then drag an InvokeVcoWorkflow object into the custom code section and attach it to the start node.  When I click on the Select a vCenter Orchestrator workflow button, I am greeted with An error occurred while processing this request and I can go no further.  The only other error I see is at the bottom where it says:

Value for a required activity argument 'VirtualMachineId' was not supplied.  I though this was passed in by default, and I can't see anywhere to add it.  I'm not finding anything in my searches, so I'm at a loss here.

Any assistance would be appreciated.

Thanks.