ManualWorkflowSchedulerService is used for synchronous execution of workflow instances. If this service is being used, the workflow instances are executed on the calling thread from the host application, thus blocking the execution of the host application until the workflow instance becomes idle.

When using ManualWorkflowSchedulerService in an WebService environment with the DelayActivity you need to set the UseActiveTimers of the ManualWorkflowSchedulerService to true and make sure the ASP.NET process is reloaded when IIS unloads it.

See also: DefaultWorkflowSchedulerService