How To Fix "This form cannot be opened. It is not workflow enabled " Error

Problem

You’ve developed a custom workflow using Windows Workflow foundation, Visual Studio, and a nice little product called InfoPath, however, when you test your workflow you get the error message "This form cannot be opened. It is not workflow enabled."

Resolution

This form cannot be displayed properly because your security level is not set to "Domain". Open the form and republish it with the security level = "Domain"