BT Wholesale "green box" error message - why, and how to fix?

[#1]

Can someone please point me to the discussion of why the BT Wholesale "green box" error message appears and what's the best way to fix it? I know there's a discussion somewhere in this forum (possibly in the big 80+ page thread) but I can't find it. I seem to remember it's something to do with the DNS, but that's as far as I can get. It wasn't a problem for me at the time when I read the discussion, so I didn't mark or note it, but recently I've been getting it quite a lot.
I hope having a thread with a relevant title will make the solution/workaround easier for others to find.
Graham

[#2]

Enter the DNS servers 212.159.6.9 and 212.159.6.10 explicitly rather than allowing the router to pick them up automatically. You could also enter them in the network settings on the PC.

[#3]

Thanks very much, jelv. Now done.
Graham