In some cases, IIS server does not manage InProc session state mode correctly. Which results in quick expiration of the login session.
Solution:Switch session state from InProc mode to State server mode.
To do that, edit myLittleAdmin web.config file
and add in the system.web section :
Code:<sessionState
mode="StateServer"
stateConnectionString="tcpip=localhost:42424"
cookieless="false"
timeout="20"
/>
Check also that ASP Net Session State service is running.