is there a setting that i am missing to prevent people from loggin in with a same username twice durring one session.

the example having multiple browsers open and accessing the asp secured content with the same username on each of the browsers at the same time.

Well, that's kind of a weird question you're asking. If its truly the same session then another window couldn't possibly make them log in again the same session because they would already be logged in.

If it did make them login it's technically another session and that behavior is all based on preference settings in the web browser. By default different windows share sessions but it can be changed.

Now there is a Concurrent Login Check in the settings.. it prevents concurrent logins by a username but only if the ips are different...if its the same IP they are going to able to do it...