D-Link DSL2640B Firmware Upgrade Problem

[#1]

I'm having what seems to be a pretty common problem when trying to upgrade the firmware on this router (supplied by PN).
I've tried pointing the update page to the .zip file to the original files and to the files renamed (just to rule out the file name length) but it always tells me to "enter a valid filename"
I've done a search already for this problem and seen a lot of others having the same issue which was resolved by using IE instead of Firefox / Opera etc.
Well I've tried using IE and Firefox but still can't get it to accept the files, tried 2 machines 1 Vista x64 IE8/Firefox and the other W2K IE6
Status for router shows "Firmware Version: 3.06 Hardware Version: B2"
Any ideas?

[#2]

I've got the self-same router model (from PN) in the last month or so.

Quote

Firmware Version: UK_3.07 Hardware Version: B2

I would have thought you needed to unzip first...
It wouldn't make any difference what kind of browser or OS was used.
A download is a download...
The manual says only upgrade firmware if Dlink or your ISP say so.
You are using a wired connection aren't you?

[#3]

I tried with the files unzipped and zipped (just in case) didn't work either way.
Browser apparently  is a known issue, I suppose due to the router interface being web based.
My line quality isn't too great and I read that this firmware will help with that, guessing that there's quite a few improvements judging by the difference in version number.
and yes I am using a wired connection .. I always do when doing any kind of firmware upgrade.

[#4]

I had a read about the problems people have with these upgrades.
I suspect that there are USA and non-USA routers (and firmwares).
Since any upgrade will carry out simple checks that a file is not corrupt, it may be that the
router is checking the file to make sure it has the right kind of nationality of the firmware.
Perhaps the message thinks you have lots of firmware files kicking around and you have chosen the wrong one?
Might be worth viewing the firmware with a binary editor to see if you can spot any kind of nationality in it 

[#5]

There is an upgrade on the D-Link USA web site. It says it may render the router unusable if I use a USA update on a non-USA product.
As I received this from PN I'm guessing that this is a UK product and should accept a UK firmware update.
The 2 upgrade files are ~3.5Mb each so a bit too much to search through.
As PN must have sent these routers out to a large number of people I can't understand how no-one come across this problem before and found a fix.