Will AJAX methods calls complete when an exception is thrown?

Question

When a menu item is clicked in my menu an ASCX control is loaded via AJAX in my asp panel. To do this I have a method:

public void LoadControl(ControlDestination controlDestination, string filename)
{
    try
    {
        // Load control from file
        Control control = LoadControl(filename);

        // Check control extends BaseForm
          // Do stuff    
        }
        else
        {
            throw new Exception("Web User Control erft niet van BaseForm.");
        }
    }
    catch (ArgumentNullException e)
    {
        // Implement
    }
    catch(HttpException e)
    {
        LoadControl(ControlDestination.Menu, "Error.ascx");
        throw new Exception("User control niet gevonden: " + e.ToString());
    }
}

When I set a breakpoint at the HttpException I get there. I press F11 and the code in LoadControl is executed. Then the excetpion pops up. All this goes well, but Error.ascx is never loaded. I know the method is working because when I want to load other ASCX objects via this method it works. But When I want to load Error.ascx is goes wrong.

I can see Error.ascx if I comment out throw new Exception("User control niet gevonden" + e.ToString()); I want both lines to be executed.

EDIT:

In my master page I have this javascript code to catch some exceptions:

function pageLoad() {
    var manager = Sys.WebForms.PageRequestManager.getInstance();
    manager.add_endRequest(endRequest);
    manager.add_beginRequest(beginRequest);
}

function endRequest(sender, args){
    var Error = args.get_error();
    if (Error != null) {
        ToggleErrorOn(true);
        document.getElementById("ErrorContent").innerHTML = Error.message;
        args.set_errorHandled(true);
    }
}

Answer 1

An uncaught exception causes the Update Panel to fail any rendering. Instead, it relays an error code back to the AJAX handler which displays the error message.

As such, if you keep throwing that exception, your Error.ascx will never get rendered.

UPDATE:

Your javascript catches the exception too late. The UpdatePanel pipeline has already considered itself in the "errored" state. Any exception thrown by your codebehind but not caught in your codebehind will cause UpdatePanel to drop all HTML it would have rendered and return a simple error code. Which your javascript function is then handling.