title: Error: "is not an attribute class" when using ConfigurationElementType attribute
body: <p>I'm trying to create a custom exception handler for the exception handling block of enterprise library 5.0.  As far as I understand I need to start the class off with the attribute 
  "[ConfigurationElementType(typeof(CustomHandlerData))]". But I get an error stating the ConfigurationElementType is not an attribute class.</p>
  
  <p>Does anyone know what might be going on?</p>