Is it possible to restrict the number of times a user can log in? By this I mean, if I have sold a single subscription to a company, can a limit the number of users in that company so that only one at a time logs in? Or two users if they have two subscriptions?

If DNN does not have this facility, is there a third party product I can use?

Thanks

the main problem is the nature of http protokoll, which does not keep a connection, i.e. you cannot say for sure, that the user hasn't logged in a second time without possibly locking the user out for a period of time. if he logs in on PC A and closes the browser, by default his entry will be removed 20 minutes later and for the time in between, he might not be able to regain access to the site, if you blocked a second connection. you may validate the IP to be the same, but some networks map multiple PCs on the same address or assign a different addess, if the user disconnects and reconnects a dialup connection.