Hello Piyush,
When an appointment spans several days it is rendered in parts. The last number in the ClientID is the appointment part index. You will receive an AppointmentCreated event for each part about to be rendered. The actual ID is the previous integer.
You should supply the complete ClientID to RadToolTip, as it is the id of the actual div element, that holds the appointment.
Best wishes,
Tsvetomir Tsonev
the Telerik team