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Locate the <system.web> section, then add this immediately beneath it: 

<system.web>
<configuration>
  <sessionstate 
      <sessionState mode="stateserverStateServer"
      cookielessstateConnectionString="false" 
      server="tcpip=127.0.0.1:42424" 
      portcookieless="42424false"
  
  timeout="20"/>
</configuration>

Then save the changes. 

At this point the application should start using the state server for storing session information - this is a resilient store that will survive when the application pool is recycled. 

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