Urgent : DLL for "RetrieveCrmTicketRequest" class in MS CRM 2011

Hello All,

Which DLL is used for class "RetrieveCrmTicketRequest". In the following code I am unable to solve the reference error:

 RetrieveCrmTicketRequest ticketRequest = 
                    new RetrieveCrmTicketRequest();
ticketRequest.OrganizationName = organization;
ticketRequest.UserId = domain + "\\" + username;
ticketRequest.Password = password;
RetrieveCrmTicketResponse ticketResponse = 
                    (RetrieveCrmTicketResponse)disco.Execute(ticketRequest);