I ran across an exception "Microsoft JScript runtime error: ‘this._postBackSettings.async’ is null or not an object" the other day while writing some AJAX code with .Net AJAX Extensions for .Net framework 2.0.
The page I was developing was simply enough, basically, it just consists of a button and a textbox inside an update panel. Doing a search on the error turned out quite a few matches, and it seems that a lot of people are having the same issue.
After reading a couple of posts, I realized that the reasons given were either incorrect (i.e. did not solve the issue I had) or pretty vague. So, after carefully looking through the exception path within the JScript library, I realized that this might have been caused by the fact that the page does not have a default submit button.
So here is the solution:
Add an asp panel around the submit button and the textbox, and set the DefaultButton property to the submit button. Now the the submit button should be working without triggering the JScript exception mentioned earlier.
<asp:Panel ID="Panel1" runat="server" DefaultButton="BtnSubmit">