Since you can't read the session variable of the client, you have to go with the method I mentioned. Let the admin inactivte the user, and store the decision in a column and check for it on the next login. The other option is to write the login information to session variable as well as a database table which can be accessed by both admin and client. To record logout, on events logout click or session_end (available in Global.asax.{
vb/cs} of your application) update the info in database as logout. This way you can check if the user is logged in or not by looking up the database.
I hope this will work for you.
Regards,
Sai Puli