Before page load, custom calendar control postbacks onclick

I have a custom calendar control on my page in one panel & in other one i have a repeater which loads the data.
Now when the page loads, first the calendar control shows up while repeater is still loading, during this if user click on calendar control then page postbacks & after that if user clicks any of the page buttons then, page crashes.
I want that till the page is loading how to disable the calendar control or else any other option?
Pls help.



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