I am having an issue with my application. The web application is quite large and works by using a number of ascx and VB server controls, each of which does various partial post backs using update panels. Everything works fine on my local machine but when I push my application to the server (IIS) I notice that my application will throw an error during an update of an update panel. This error is intermittent but will occur, eventually, if I use enough of the controls on my page that causes partial postbacks. Here is the error:

Code:
Sys.WebForms.PageRequestManagerServerErrorException: Object reference not set to an instance of an object.
I'm not sure what is causing this error or how to track down which control is causing this problem. I've tried debugging the live application using IE's Developer Tools. The error seems to be originating from a web resource, MicrosoftAjaxWebForms.debug.js. The function that is having the problem is:

Code:
_endPostBack: function PageRequestManager$_endPostBack(error, executor, data) {
    if (this._request === executor.get_webRequest()) {
        this._processingRequest = false;
        this._additionalInput = null;
        this._request = null;
    }

    var eventArgs = new Sys.WebForms.EndRequestEventArgs(error, data ? data.dataItems : {}, executor);
    Sys.Observer.raiseEvent(this, "endRequest", eventArgs);
    if (error && !eventArgs.get_errorHandled()) {
        throw error;
    }
},
The data variable is coming across as null. Anyone know how to address this problem or how to find out specifically which control on my page is causing the issue?

This causes the above error and, worst, stops all updatepanels's partial postbacks from working until the page is refreshed. I an able to trap the error like this:

On the page with the scriptmanager (its a master page):

Code:
Protected Sub ScriptManager1_OnAsyncPostBackErro(ByVal sender As Object, ByVal e As AsyncPostBackErrorEventArgs) Handles ScriptManager1.AsyncPostBackError
    ScriptManager1.AsyncPostBackErrorMessage = e.Exception.Message
End Sub
In it javacript:

Code:
    function pageLoad() {
        Sys.WebForms.PageRequestManager.getInstance().add_endRequest(onEndRequest);
    }

    function onEndRequest(sender, args) {
        if (args.get_error() != undefined) {
            var msg = args.get_error().message;
            var sen = sender.id;

            alert(msg + ' Sender: ' + sen);
            args.set_errorHandled(true);
        }
    }
But the error still stops all update panels on my page from working. Does anyone have any insight or suggestions?

Thanks
jason