Session variables getting 'lost'

I have created an intense web application that makes sure of many frames. One of the frames at the bottom of the app refreshes every 30 seconds, this does 2 things...

1.) It keeps the user's session alive even if they are not at their PC
2.) Refreshes the user's data/checks in the database for new information and pops it up to the user...

Now on one or two of our employees browsers, sometimes the page that refreshes just turns white and doesn't reload, thus the user loses session information and is logged out. Or the page just gives a page cannot be displayed error, with no other error detail...

The browser is handling large amounts of data, including an ActiveX control that has all the user's email in a certain folder. So there can be megs of data in the ActiveX control.

Why should some computers have this problem, but not others? How can session variables just be lost? I checked in the Event Log and the asp.net worker process is definately not restarting...

Well since this seems to be only a problem with some user's browsers and not others, I'll write it off as a browser bug. So to fix it I just set cookieless = 'true' in the web.config, problem fixed..

Another interesting article I read on MSDN stated that session varaibles could be lost when virus scanners were opening and reading web.config files and then the datestamp marked it as modified, thus losing session info.

So if you are having this prob, configure your virus scanner to not scan *.config and *.asax files...