We responded to you in the support ticket with ID 651963 for the same issue. Could we continue the discussion there?
I will post the response from that thread here too in order for it to be available for the community:
In order to access the DisplayDateChanged event of the Calendar in the DateTimePicker control you should use the Style of the RadDateTimePicker not the CalendarStyle. Placing RadCalendar control in the Template of the RadCalendar is not a supported scenario in the control.
All the best,
the Telerik team