Debug Custom Workflow with Plugin Reg Tool

I'm having some difficulty using the plugin Reg Tool to debug a very simple custom workflow activity I've created.

PLugin Reg Version: 7.0.1.129

CRM 2015 Prem

I've created a sample workflow that runs my Custom Workflow Activity and when I try to profile this workflow the "steps" section shows up blank

If I try to save the profiler settings I get this error

"Unhandled Exception: System.ArgumentNullException: Value cannot be null.
Parameter name: workflowSteps
   at PluginProfiler.Library.ProfilerManagementUtility.EnableWorkflow(CrmServiceClient service, String overrideKeyFileName, Guid workflowId, Boolean persistToEntity, String persistenceSessionKey, Boolean includeSecureInformation, Boolean isContextReplay, CustomActivityStep[] workflowSteps)
   at Microsoft.Crm.Tools.PluginRegistration.ProfilerSettingsViewModel.btnOk_Click()"

I'm using the instructions posted here:

http://blogs.microsoft.co.il/rdt/2013/03/08/debugging-workflow-custom-activities-with-plugin-registration-tool/

Any suggestions are appreciated.  I'd prefer to debug this way vs attaching to the IIS process.