+2  A: 

What is the DOCTYPE of the page? Also, what browser is it? I have seen this issue on pages with invalid/old DOCTYPEs with IE6-7 in Quirks mode.

In quirks mode, javascript values(like scroll position), can be off, resulting in a bad render. You should ensure you have a valid DOCTYPE that forces IE into standards mode like..

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;
Jab
The page did not have a DOCTYPE. I added the DOCTYPE from above and this fixed the issue. Thanks!
Kyle Trauberman
A: 
A: 

I also have this issue. I have the correct DOCTYPE, but my page opens in jQuery blockUI (modal popup). The calendar renders fine, but if you scroll and then try to show it, it displays in the wrong position.

im
A: 

I came across the same problem today.

The solution, while somewhat difficult to find on the web, is rather trivial

Create a new Div with its position set to relative (style="position:relative;")

and place your textbox and calendarExtender inside the Div.

That fixed the problem i was facing, i hope it does the trick for you too

Dogoku