title: Sharepoint users are logged out
body: <p>Everyday at sometime (mostly near the noon) all users of our sharepoint (2007) except "System Account" automatically get logged out and cannot login for about 30mins.
  I have no idea what possibly causes this situation. Can anyone help?</p>
  
  <p>Thanks in advance.</p>
  
  <p><strong>Update:</strong> we use Active Directory for user authentication. At situations described above we can successfully login to Active Directory but it seems that SharePoint fails to login.</p>