It doesn't matter what browser or what machine on this particular network we use, we cannot access certain webpages or download certain files. The browser will just sit there loading permanently and never load the page or go to the standard error of not being able to load the page. Sometimes we will get the title bar showing the title name or the favourite icon showing, but nothing else. What is weird is that we can access different pages on these sites (for instance, we can access a HTTPS page on the same site where we cannot load the HTTP mainpage, or for another site we can load a page on a site, but not initiate a download of a file from the same site). We have tried changing the MTU on the router (Cisco 1841) and checking for malware on multiple machines with multiple different antimalware products. Internet Explorer 7, 8, 9, Firefox 3.6, 4, 5, Google Chrome. Server 2008, Windows 7, Vista, XP. All produce the issues. We have tried rebooting the router, switches and servers. A traceroute works fine, loading the pages via IP address or hostname works outside of this network, but produces the above issues within the network. Any help will be greatly appreciated.

One more thing can be done connect your computer directly to the fast ehternet port of the router and give a try and also make it sure you dont have any virus on your connected pc or laptop. If the issue still exists then you might have to seek help from you ISPhttp://www.virmansec.com/blogs/skhairuddin

Thanks; I will have to give that a go. The ISP denies any issues exist. I have already tried to contact them with this same information.

Thanks for your help and increase in confidence that I was right all along. I changed nothing, yet when I checked today, after a few months of having this issue, it dissappeared and all was good. I belive the ISP has done something. I have emailed asking for an explanation because they denied responsibility in the past, yet nothing has changed on the network or on the other side (websites in question).

I am really glad that you have solved the issue.http://www.virmansec.com/blogs/skhairuddin