You create a Microsoft ASP.NET application by using the Microsoft .NET Framework
version 3.5.You create a Web form by using ASP.NET AJAX.You write the following
client-script code fragment to handle the exceptions thrown from asynchronous postbacks.
(Line numbers are included for reference only.)
01 <script type=”text/javascript”>
02 function pageLoad()
03 {
04 var pageMgr =
05 Sys.WebForms.PageRequestManager.getInstance();
06
07 }
08
09 function errorHandler(sender, args)
10 {
11
12 }
13 </script>
You need to ensure that the application performs the following tasks:
Use a common client-script function named errorHandler.

Update a Label control that has an ID named lblError with the error message.
Prevent the browser from displaying any message box or Javascript error.
What should you do?

A.
Insert the following code segment at line 06.
pageMgr.add_endRequest(errorHandler);
Insert the following code segment at line 11.
if (args.get_error() != null) {
$get(‘lblError’).innerHTML = args.get_error().message;
args.set_errorHandled(true);
}

B.
Insert the following code segment at line 06.
pageMgr.add_endRequest(errorHandler);
Insert the following code segment at line 11.
if (args.get_error() != null) {
$get(‘lblError’).innerHTML = args.get_error().message;
}

C.
Insert the following code segment at line 06.
pageMgr.add_pageLoaded(errorHandler);
Insert the following code segment at line 11.
if (args.get_error() != null) {
$get(‘lblError’).innerHTML = args.get_error().message;
args.set_errorHandled(true);
}

D.
Insert the following code segment at line 06.
pageMgr.add_pageLoaded(errorHandler);
Insert the following code segment at line 11.
if (args.get_error() != null) {
$get(‘lblError’).innerHTML = args.get_error().message;
}

Explanation:
The errorHandler must be registered with end_Request and set_errorHandled must be set to true, thereby eliminating all answer choices except for answer choice A.

Sys.WebForms.EndRequestEventArgs errorHandled Property http://msdn.microsoft.com/en-us/library/bb397429.aspx
http://encosia.com/2007/07/18/how-to-improve-aspnet-ajax-error-handling/