How to suppress windows security popup when an application pool timeout expired

We just updated and rebuilt our web site from framework 3.5 (using Visual Studio 2008) to framework 4.5 (using visual studio 2012). It is also being hosted under a new version of windows server (moving from windows server 2003 with IIS6 to Windows server 2008 R2 with IIS7.5). I am using ASP.NET V4.0 Classic mode and Windows Authentication for this web site. The Session State settings are:  Mode: In process, Cookie Setting: Use URI with both check boxes for "Regenerated expired session ID" and "Use hosting identity for impersonation" checked. Right now if the web application is seating idle for more than 20 minutes then the application pool idle timeout kicked in and a windows security popup to ask the user to enter their windows credential in an infinite loop. The only way the get out of this loop is to selected Cancel from the windows security popup and close the browser. I do not know why it does that? so What am i doing wrong? How d ...