As you can see my ajax calender positioning is not below of the textbox of "Date of Birth".
This webpage is consist Javascript which applied scrolling animation by clicking each of the sub menu at the left instead of post back.
Here is my asp.net code

<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server" />
<asp:Label runat="server" Text="Date of Birth: " />
<asp:TextBox ID="txtDOB" runat="server" />
<asp:CalendarExtender runat="server" TargetControlID="txtDOB" TodaysDateFormat="d MMMM, yyyy" Format="dd/MM/yyyy" />

Any problems?

I don't know asp but I think in your css you set you calendar to an absolute positioning and that could be your problem,but if I can't see the live site.
I can only recomand you to chech the positioning, if it is absolute than changeit to relative and see if that is the problem.
Hope this helps

commented: Good answer +2

The solution to this problem is definatley going to be styling related. If you can right click on the page and view source, you may be able to figure out why its positioned there.

In my case, I am unable to reproduce this because I dont have the ajaxtoolkit installed. I'm pretty confident the calendar is rendered within a div element. Take a look at the id of that element. Once you have that, you should be able to control its display and positioning.

i check for the styling already, even though i made some changes for the styling but it still can't work.

LoL. The biggest jokes ever. :/
Just find the div id and add a position: relative like dany12 said, and it work fine already. This issue costs me few weeks already. -o-?
Thanks in anyway. :)

Glad to hear you resolved it.