Hi Vince,
Could you please clarify what action you actually perform with the popup, that is, which property of which object you check?
Anyway, working with an object which only exists for a few seconds is probably not a very reliable approach, because TestComplete might not have enough time to update the objects tree accordingly. If you want to use this window for downloads progress detection, you should probably try waiting for the window's appearance as described in the
Checking Whether an Object Exists help topic. Another possible approach (which seems much more reliable for me) is to work with the downloads window which actually displays the download progress bar.