ASP.NET

try
{
    string fileName = fuFileUpload.PostedFile.FileName; (THIS IS WHERE IT FAILS...)                string contentType = fuFileUpload.PostedFile.ContentType;
    string getFileName = System.IO.Path.GetFileName(fileName);
    string userName = Page.User.Identity.Name;

    Stream fileStream = fuFileUpload.PostedFile.InputStream;
    Byte[] fileBuffer = new byte[1024];

    while (fileStream.Read(fileBuffer, 0, fileBuffer.Length) > 0)
    {
        fuFileUpload.PostedFile.SaveAs(Server.MapPath("UploadedFiles\\") + userName + "_" + getFileName);
    }

    fileStream.Close();
    lblProgress.Text = UploadSuccess;

    //Response.Redirect("UploadFiles.aspx");
}
catch (Exception ex)
{
    ex.Message.ToString();
}

 function OnPageLoad()
{
    // OnPageLoad() is defined in _smfcommon.js, which is included in all pages.
    // We override it here so we can use the EndRequestHandler and InitializeRequest functions
    // in this page.

    // Add initializeRequest and endRequest
    Sys.WebForms.PageRequestManager.getInstance().add_initializeRequest(InitializeRequest);
    Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);

    return;
}

// Called when async postback begins
function InitializeRequest(sender, args) {
    alert("You are in the InitializeRequestHandler function.");  // breakpoint here
}

// Called when async postback ends
function EndRequestHandler(sender, args)
{
    // this function is run after an Ajax partial postback occurs

   alert("You are in the EndRequestHandler function.");    // breakpoint here

   if (args.get_error() != undefined)
       alert("There was an error" + args.get_error().message);
   
    return;
}