[Please forgive if everyone already knows this, but it has been a source of frustration for me until I finally figured it out!] In a separate thread ( http://www.elitetrader.com/vb/showthread.php?s=&threadid=93898 ) and also as a feature suggestion, I had observed a behavior whereby retrieving successive time & sales data via TWS fails, and you get nothing. I also observed that the issue seems to be less within the past few wks, but after some more experimentation, I now understand what is really going on. It appears that there is an intentional throttle on how many requests you can submit to the IB historical data servers in a given amount of time! From experimentation, it looks like after approx 20 requests, it freezes you for approx 5 minutes. I can understand the need to limit historical data retrieval (since IB does not profess to be a true historical data source), but my concrete suggestions would be: 1. Allow a higher limit for time & sales because esp with a thinly traded stock, one tends to want to explore around unusual spikes/etc. 2. Have an explicit error messaging informing the user so the user doesn't think the system is defective. 3. Consider lowering the 5 minutes to say 1 minute -- I think it's really programatic high volume sucks we want to avoid, not users hitting Next on the T&S page. I sitll think recently the situation has improved, possibly because the ~20 limit was increased from a smaller number?