Going to try and add some information, and answer your questions: Could it be some conflict with the Hosts file: To my knowledge the host file in C:\Windows\System32\Drivers\etc\hosts is configured correctly. It hasn't been touched in 2 years. Checked it again just to make sure, and it looks good. Is there any chance that the addresses have been added in IE "Internet zone": Great point. Higher level GPO's are preventing me from checking the actual Internet Options, however I was able to run a gpresult, dump it to a html file, and check the GPO settings from the domain. It seems the the sites are only being listed in the HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings -> ProxyOverride as a REG_SZ. Can you run a trace route in the various cases (particularly the one with the 25 seconds delay): Yes. Traceroutes and Pathpings indicate that each hop is responding within ~1ms. Is the behaviour the same if you use web addresses like http://myniceweb/mypage.htmand iP addresses like http://192.168.0.100/mypage.htm : Those pages I was not able to visit. But I instead used google.com and 74.125.228.193 which is a google.com server. Both responded very promptly (1-2 seconds) I.e. could it be related to a DNS issue of some kind, are the result of running nslookup correct?: Nslookup on the URL/IP both match backwards and forwards. Is it possible that one of the Windows updates in the last two months caused this?: We have tried old VHD files (vDisk in our Citrix environment) that were 5 months old, attached to an empty Virtual Machine, logged in and it didn't work... so probably not a patch or a GPO (as hard as that is for me to say... gahh...) One thing someone in another shop sugggested us trying is setting the Local Intranet security settings from Medium-Low to Low. I also read about this online, as it might be specific to Citrix. I got the go ahead, but it seems every single thing I try either GPO or Local Policy will not change the Internet Options > Security Tab > Local Intranet > Security Level = Low . I have dug through the registry, and dug through the gpresult i exported to an html file, and can't find what is making it greyed out and preventing me from changing it. I changed it on the local level also i.e. local machine policy, but no luck. Any idea on how I can change the Local Intranet security settings from Medium-Low to Low? Weird as it sounds, from what I read online and from what someone in another shop told me, this might do the trick.