Can’t access wp-login.php, admin section when behind an ISA firewall (solution)

Hi,
I have recently moved my WP blog to another site which requires me to access the site via the internet rather than the intranet which I did previously.
Once I had done this I found that everyone in my company could view the site fine but only some users could access wp-login.php and log in. For everyone else the page would never load and hang. Our company sits behind an ISA 2000 firewall which gives our internet access.
I searched all over these forums and found similar issues but none related to ISA firewall. I found that everyone else outside of our company (which did not have an ISA) worked fine. This solution may work on other environments but I have not tested this on anything other than the following:

An ISA 2000 firewall
Client machines using IE 7 configured as a webproxy to go through the ISA Firewall for internet access.

I suspect that the problem lies with ISA 2000 not recognising PHP sites properly (with ISA being dated now).
On each machine experiencing the problem you need to go to Tools > Internet Options.
Click the Advanced tab. You will a load of tick boxes. Scroll down until you see the section “HTTP 1.1 Settings”.
The second tick box “Use HTTP 1.1 through proxy connections” will most likely be ticked, untick it and all should work ok.

Reason (My Theory!)
Because the client browser (in this case IE 7) has been configured as webproxy client it forces the browser to use HTTP 1.1 which (I am presuming but not confirmed) has issues with PHP. By turning this off it will work.
I swear I have been pulling my hair with this one for ages and thought I would post this here because I have seen a lot of similar problems still with no resolutions yet.
Try this one, it might work!