The sessionState tag in the web.config files allows to control the session
timeout but typically it should be set to the lowest value that fits your
needs, not to an excessive or infinite value...
I believe you have some other kind of problem you should workaround another
way. For example, permanent values should be IMO best stored in a "user
profile" stored in the database rather than to be kept "permanently" in an
infinite session (you can however "cache" these values as session variables
if needed)...
Patrice