It was pointed out to me that only 5 concurrent Workflows are allowed, and to fix it : In the Program file, import the System.Workflow.Runtime.Tracking namespace so that you can use the types in that namespace. C# Copy Code using System.Workflow.Runtime.Tracking; In the Program class, create a static Int32 field named maxSimultaneousWorkflows, and assign it the value 1. C# Copy Code static int maxSimultaneousWorkflows = 1; In the Main method that is defined in the Program class, add the DefaultWorkflowSchedulerService to the WorkflowRuntime. Use the AddService method, and pass the number of maximum simultaneous workflows that the DefaultWorkflowSchedulerService can schedule as a parameter. C# Copy Code workflowRuntime.AddService( new DefaultWorkflowSchedulerService(maxSimultaneousWorkflows)); Note, this was copied directly from the help file....