When I make a change to the schedule, or if I view the AdvancedEditForm for a particular appointment, I start getting the following error when I hover over an appointment:

Unable to get value of the property 'get_allowDelete': object is null or undefined

If I add a new appointment the page refreshes (via Ajax, not a full postback).  I can hover over the new appointment without a problem, but any existing appointments will throw this error.

When I step through the JavaScript debugger, I see that there is a call to get_element(), and this method looks in the first position of the _domElements array.  In my case, the first entry is null, but the second contains the element that it should be returning.

Hello Chet,

I did not manage to reproduce the described behavior. I tested the get_allowDelete() and get_allowEdit() methods of the appointment client-side object and everything worked as expected.

Could you please provide me with some more information about the issue in question? You could send us a support ticket with a sample page illustrating the issue attached to it, so we will be able to troubleshoot that kind of a behavior locally. 

Thank you in advance.

Regards,
Ivana
the Telerik team

Sorry, I thought I had closed this question.

I had a custom ScheduleProvider which was caching the appointment objects.  After a more careful examination of XmlScheduleProvider, I noticed that new Appointment objects need to be created every time GetAppointments is called.  If you don't do this, the AppointmentControls collection fills up with out-of-date entries which cause get_allowDelete to break.