Non-modal dialogs are not supported. RadScheduleView dialogs put the corresponding appointment in edit mode and since you cannot have multiple appointments in edit mode you cannot have several dialogs open simultaneously.
You can try creating a non modal dialogs if you replace all of the dialog logic in RadScheduleView - cancel the ShowDialog
event and do everything by hand. But this is a lot of work and it is possible that you will hit other obstacles.
You can refer to the links below for more details about customizing the dialogs
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