Following error comes when I leave page for a few hours

Hi,I am using AJAX Toolkit Controls as well as AJAX in my page. When I change tabs in my page I get this error .Is there any solution for this. I am making a call to Response.Write which I cannot change but this behaviour does not occur in normal operations of the web application.--------------------------- Windows Internet Explorer --------------------------- Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled. Details: Error parsing near '<HTML><HEAD><TITLE><'. --------------------------- OK ---------------------------
 Thanks
&nbs ...