Response.Redirect Holds Other Pages from Loading

Here's the scenario.
I've got a form with a button on it. You have to be logged in to see this form. I use this code to check if the user is logged in and act appropriatley.
Dim isLoggedIn As Boolean = CType(Session("LoggedIn"), Boolean)
       

        If isLoggedIn = False Then
            Response.Redirect("Login.aspx")
        End If
The button runs a report that takes anywhere from 0.5 to 20 seconds. For testing it just sleeps for 10 seconds.
Threading.Thread.Sleep(10000)


The problem is this. Say User1 comes to the form, logs in and runs the report. If User2 comes to the form, the page will not load until User1's report is done.
Now, t ...