How to restrict no of user registrants in a day in asp.net

oid Application_Start(object sender, EventArgs e)
{
    Application["ActiveSessions"] = 0;
}

void Session_Start(object sender, EventArgs e)
{
    try
    {
        Application.Lock();

        int activeSessions = (int) Application["ActiveSessions"] + 1;
        int allowedSessions = 10; // retrieve the threshold here instead

        Application["ActiveSessions"] = activeSessions;

        if (activeSessions > allowedSessions)
            System.Web.HttpContext.Current.Response.Redirect("~/UserLimitReached.aspx", false);
    }
    finally
    {
        Application.UnLock();
    }
}

void Session_End(object sender, EventArgs e)
{
    Application.Lock();
    Application["ActiveSessions"] = (int)Application["ActiveSessions"] - 1;
    Application.UnLock();
}