Error when acessing a RESTEasy resource method: "Could not find MessageBodyWriter for response object of type" or "Could not find MessageBodyReader for response object of type"

Issue

• I am getting the following error about MessageBodyWriter when trying to access my RESTful WEB Service:

   ERROR org.jboss.resteasy.core.SynchronousDispatcher - Failed executing GET /{your context}
   ERROR [STDERR] org.jboss.resteasy.core.NoMessageBodyWriterFoundFailure: Could not find MessageBodyWriter for response object of type: {your bean/POJO class} of media type: {Media type requested}
  

• I am getting the following error about MessageBodyReader when trying to access my RESTful WEB Service:

  ERROR org.jboss.resteasy.core.SynchronousDispatcher - Failed executing POST /{your context}
  ERROR [STDERR] org.jboss.resteasy.spi.BadRequestException: Could not find message body reader for type: class {your pojo} of content type: {Media type requested}