Sorry for the confusion: You are correct - it should be ModalPopup.Show() rather than pnlPopup.Show().
I have re-created the sample project using Visual Studio, .NET Framework 3.5, the latest Ajax Control Toolkit and the latest DayPilot Pro (7.7). You can download it here:
http://code.daypilot.org/57459/event-calendar-and-modalpopupextender
The tutorial describes the key parts of the code (both the .aspx and the code behind).
The sample code is simplified:
- it doesn't use DetailsView (the DetailsView binding logic adds complexity)
- there are separate dialogs for event creating (ModalPopupCreate) and editing (ModalPopupEdit)
If the modal popup displays at the right time (on time range selection) but at the wrong place you may need to review the CSS and/or placement of the Panel with the dialog content. If you use complex page layout it may affect the correct placement (normally it should be re-positioned automatically using the ModalPopupExtender).
I would recommend trying it on a blank page (like in the updated tutorial) or to disable the global CSS styles temporarily to see if it makes any difference.