There is a bug in ESB Toolkit 2.1 when navigating generic ESB.ItineraryService.Generic.Reponse.WCF service, you get the following error:
Microsoft.Practices.ESB.ServiceModel.Helpers.Exceptions+SoapHeaderExtensionException: Error 855000: Could not find schema file for SOAP header ‘ItineraryDescription’ at path C:\Program Files (x86)\Microsoft BizTalk ESB Toolkit 2.1\Web\ESB.ItineraryServices.Generic.Response.WCF\App_Data\ItineraryDescription.xsd
To make it work, you have to get the ItineraryDescription.xsd file from a Non-generic service, in my case I got it from the path in C:\Program Files (x86)\Microsoft BizTalk ESB Toolkit 2.1\Web\ESB.ItineraryServices.Response.WCF\App_Data\
Just copy the file ItineraryDescription.xsd from there and Paste it to C:\Program Files (x86)\Microsoft BizTalk ESB Toolkit 2.1\Web\ESB.ItineraryServices.Generic.Response.WCF\App_Data\
Then do a Recycle of the pool under which the service is running, in my case the pool is CoreEsbWcfAppPool. After that ,do a browse again of the ESB.ItineraryService.Generic.Reponse.WCF service and it should be working already.