By default, worker processes recycle after 120 minutes. If your ASP applications are not designed to store session state while a worker process is recycled, then session state in that ASP application can be lost. To remedy this problem, you can either store session state in a database or disable worker process recycling.
To disable worker process recycling
¬†¬†¬†¬†In IIS Manager, expand the local computer, expand Application Pools, right-click the application pool, and then click Properties.
¬†¬†¬†¬†On the Recycling tab, clear the Recycle worker processes (in minutes) check box.