We have had this problem on and off for the past couple weeks. We are able to get to some sites and not to others. Seems to be mostly on Windows XP systems. Again, some systems seem to have more trouble than others. All of our Windows 7 systems are fine. No problems getting to the internet and viewing all sites. We have a Cisco router from CableVision, WatchGuard 750e XTM appliance and two Asante 48 port Switches. We have rebooted all of these a couple of times and it seems to help. Everybody seems to be working fine and then a day or so goes by and people start to call that they cannot get to some sites. This happens with all browsers. Any ideas would be much appreciated.