Hi,
Thank you very much for your business. The CalendarPopup is an advanced control that is initially invisible. The purpose of the control is so that you can "show" it with JavaScript whenever you need to, here is an example of how it is used:
http://demo.essentialobjects.com/Demos/Calendar/Features/Popup%20Calendar/Demo.aspxThis page has a single CalendarPopup control. It is not visible until one of the link is clicked (at which point the link calls some JavaScript code, which calls the CalendarPopup's client side API to display the popup). You can take a look of the sample source code to see how it works.
If you just wish to use a regular calendar or drop down date picker, you would use Calendar or DatePicker control respectively.
Hope this helps. Please feel free to let us know if you have any more questions.
Thanks!