Atlas Update Panel Problem

[Kürþat]

Hi,

I use Atlas Update Panel in an ASP.NET application. I have a control (Chart)
on update panel and I update this control every time a user select a value
from a dropdown list. So I set trigger attribute of panel as
OnSelectedIndexChanged event of dropdownlist. When I select an item from
dropdown "Object refence is not set to an Object instance" error occurs. I
try same thing with Button, it works. What should I do?

Thanks in advance.