"Could not connect to remote server"

I had started to see this error message when browsing, but only on the MacBook (the desktop didn't at all show these problems)
I saw them in 3 places:
1) When calling certain web-pages (e.g. my.opera.com)
2) Some, but certainly not all, ads on some web-pages
3) One Google gadget always gave this problem on the MacBook (Track IP Address, ISP, Country, Proxy)

The exact same problem occurred in both Opera 9.25 and Firefox 2.0.0.6
I posted to both the Opera forums and Firefox forums but nobody replied. This usually means the problem is rare or even unknown -- or it could just mean that nobody knows how to solve although even in this case somebody is likely to say just that.

I deleted ~/.opera/opera6.ini and rebooted but, while this brought things back the first time I did it, the second time it made no difference at all.

OK, so it seemed like the problem was some kind of configuration mixup on the MacBook so I decided to re-install Gutsy (Ubuntu 7.10). Note that Opera 9.25 worked fine on other OSes on the same MacBook.
So, after the re-install everything is back to normal which to me strongly indicates that this was indeed some config problem.

I'm going to summarise the other things I needed to do to get Ubuntu back to exactly where it was before I reformatted the / directory (of course, I didn't touch the /home directory).

1) Used this guide to install compiz-fusion
(Step 3 only) and then followed this thread to get fusion-icon back. I had tried another guide (mentioned in thread) that gave a funny-looking fusion-icon icon that I wanted to change.

2) Wireless was very easy to get back using this guide.
Note that I did not at all have to install either NetworkManager or nm-applet.

3) AWN came back by just using this guide. Note that for AWN to get back its launchers, you need to start the launch/taskmanager applet.

4) Before starting, I, of course, copied the famous 4 files menu.lst, sources.list. fstab and xorg.conf to the Sidux partition so I could have them after the re-install. Actually, up to now, I have only used the menu.lst file.