HTTP 404 - File not found

[Duncan Rounding]

To recap I understand you only have a problem with some sites (at least yours). You have set the DNS in the General Tab of TCP/IP to use a fixed DNS address - entered one that Plus Net gave you and yet the problem persists. To confuse matters further your brother, also on Plus Net, has no problems.
After trying your brother's DNS why not try some of the public servers from this page:
http://www.petercooper.co.uk/archives/001086.html

Edit: I wonder if this might be a PlusNet proxy server issue?....
You might (although doubtfully) be able to bypass it by refreshing the web page by pressing Control-F5 in IE.

[Duncan Rounding]

You could also try the following (It might help to see if it is a DNS or Cache (Proxy issue)):
Start|Run - cmd (enter)
ping www.myproblemdomain.co.uk (enter)

If it responds with some lines including the sites IP then DNS worked and it may be a proxy server caching issue. If it responds with could not find host then it would seem to point to DNS.

[chrismorris2000]

PROBLEM RESOLVED !!!

It appears that on our small business server setup we had 2 network adaptors specified. One for the internal network and another for access to the internet via the router.

I was changing the DNS settings on the internal network adaptor so consquently it had no affect.

If you think you are having the same problem and you are using a small business server network the solution was :

Open up TCP/IP Properties (Control Panel | Network Setup)
Select IP address TAB
Select the adaptors drop down and see if there is more than one specified.
If so select the other adaptor.
Click on DNS tab and change settings

[wjcampbe]

Hmmm - I named the server Network connections LAN and WAN, plus of course, a quick status check shows the widely disparate IP addresses.