Hi all, i need to send http erros to external...so how can i with the following code....

global class InboundLinxUserRegistration {
     global class dtRegistrationInput {
       webservice ID UserId;
       webservice String First_Name;
       webservice String Last_Name;
       webservice String Email_Address;
       webservice String Status;
       webservice ID Workplace_Id;
       webservice String Workplace_Name;
       webservice String Workplace_Province;
       webservice String Workplace_City;
       webservice String Workplace_Postal_Code;
       webservice String Workplace_Address;
       webservice String Speciality;
       webservice String Record_Type;
      }
     global class dtRegistrationOutput {
       webservice date mydate;
       webservice String added;
       webservice String status;
       webservice String Message_Text;
       webservice String error;
      
      }
     
      public webservice static dtRegistrationOutput userregistration(dtRegistrationInput userregistration){
           dtRegistrationOutput retvalue=new dtRegistrationOutput();
           for(List<Account> account :[select National_Code__c,PersonEmail from Account]){
              for(Account acc : account) {
                 if((acc.National_Code__c==userregistration.UserId)||(acc.PersonEmail==userregistration.Email_Address)){
                         retvalue.status='Failure';
                         retvalue.Message_Text='Duplicate User';
                    }else {    
                     acc.National_Code__c=userregistration.UserId;
                     acc.FirstName=userregistration.First_Name;
                     acc.LastName=userregistration.Last_Name;
                     acc.PersonEmail=userregistration.Email_Address;
                     acc.Account_Status_NES__c=userregistration.Status;
                     acc.Primary_Parent_vod__c=userregistration.Workplace_Id;
                     acc.Primary_Province_NES__c=userregistration.Workplace_Province;
                     acc.Primary_City_NES__c=userregistration.Workplace_City;
                     acc.Primary_Postal_Code_NES__c=userregistration.Workplace_Postal_Code;
                     acc.Primary_Address_1_NES__c=userregistration.Workplace_Address;
                     acc.Specialty_1_vod__c=userregistration.Speciality;
                     acc.RecordTypeId=userregistration.Record_Type;
                     try{
                         insert acc;
                         retvalue.added='True';
                         retvalue.Message_Text='Registration Successfull';
                        } /*catch(DMLException e) {
                             retvalue.mydate=system.today();
                             retvalue.added='false';
                             retvalue.Message_Text=e.getMessage();
                        }*/
                        catch (Exception e){
                          retvalue.mydate=system.today();
                          retvalue.added='false';
                          retvalue.Message_Text=e.getMessage();
                         }
                    
                 }
              }
             return retvalue;
           }
            
                                 
          return retvalue;
       }
  }