Set DisplayErrorDlg to indicate whether you want the action to respond when the target client dataset encounters an OnReconcileError event.  

When DisplayErrorDlg is true, TClientDataSetApply is informed when the target client dataset encounters update errors and responds by calling the HandleReconcileError function. The resulting choice of reconcile action is used to initialize the Action parameter of the client dataset's OnReconcileError event handler if it exists. If the client dataset does not have an OnReconcileError event handler, the chosen reconcile action determines the client dataset's response to the update error. 

HandleReconcileError 

OnReconcileError