Workflow Foundation supports hosting workflow services outside of Internet Information Services and the Windows Activation Service via System.ServiceModel.Activities.WorkflowServiceHost. In .NET 4.5 Beta, Workflow Foundation supports C# expression syntax in workflow definitions (.xamlx files). These workflow services work as expected when hosted in IIS or WAS. However, workflow servcies using C# expressions hosted in user processes consistently throw FaultExceptions, not matter how simple the workflow. VB services work as expected. Reference this MSDN forum thread: http://social.msdn.microsoft.com/Forums/en-US/wfprerelease/thread/129405f7-0334-4011-b7b7-3afdb8693c8b.