Ajax Calendar Extender popup position is not correct when i used in update panel

Hi,

I am using Ajax calendar externder in one of my web page inside the update panel. I have problem when user click on the textbox calender popup top left corner of the page. not exactly bottom of the text box. I am not using any style or css for textbox and calendar extender.

I have try with specify the popup position but its not working. I dont know what the problem but its really important for me because its really irretate for my customer.

One important note when i click first time on the text box popup open at upper left corner of the page. but when i click on second time on the textbox its popup exactly under the textbox.