"The conversation that is being bound already exists" Exception on sending IM to multiple users

hi all ,

            I am trying to send an IM to multiple users using UCMA,

below is my code

 foreach (string useruri in _Users)
                {

                  ConversationSettings convSettings = new ConversationSettings();
                 convSettings.Priority = _conversationPriority;
                 convSettings.Subject = _conversationSubject;
           
                 Conversation conversation = new Conversation(_userendpoint, convSettings);
                 InstantMessagingCall _instantMessaging = new InstantMessagingCall(conversation);
            
                 _instantMessaging.StateChanged += this.InstantMessagingCall_StateChanged;
           
                 _instantMessaging.InstantMessagingFlowConfigurationRequested +=
                     this.InstantMessagingCall_FlowConfigurationRequested;
              
                 _instantMessaging.BeginEstablish(useruri, new ToastMessage("Hello Toast"), null,
                        CallEstablishCompleted, _instantMessaging);

                }

but for the second Iteration , its giving an Exception as "The conversation that is being bound already exists" on the line

"Conversation conversation = new Conversation(_userendpoint, convSettings);"

can anyone plz suggest how get rid of that , and send a single IM to Multiple users.