Firewall Causes Screen Freeze (clean Vista install)

Summary:
Re-installing Vista on new hard disk.
Only software installed is default Windows (through Updates) and CIS Free.
If firewall is active, screen will freeze within a few minutes of logging on.
There is no CIS popup to request user input.
Only recovery is to shutdown by pressing power button.

What aspect of firewall is causing the screen freeze?

S/W Installation:
1 - Vista Ultimate 32bit installed to empty hard disk from CD, with network cable disconnected.
2 - CIS installed from CD and configured according to instructions by Chiron.
Full installation but WITHOUT Geek Buddy.
Essentially configuration is as default, with changes: Proactive Security; HIPS Disabled; Firewall = Stealth Ports Block + boxes checked for: “Filter IPv6 traffic”, “Block fragmented IP traffic”, “Do Protocol Analysis”, and “Enable anti-ARP spoofing”.

3 - Network cable connected; CIS Quick and Rating Scans run. (All clear.)
4 - Windows Update allowed to ‘do its thing’: repeated manual checks and reboots to install 3-400 updates, taking 6-8 hours (unfortunately I am starting from an SP1 source)
5 - No problems encountered until the last 3 or 4 updates, which were (coincidentally?) Security Updates, when the freezes started to occur.

How to see freeze:
1 - Log-in as normal
2 - Start Task manager to display processes for all users
3 - Wait
4 - Screen freeze will occur within 5-10 mins, or less

Symptoms:

  • No user input is required to trigger the screen freeze (although it does seem to accelerate the problem!)
  • Task Manager stops updating – usually the first clue that freeze has occurred
  • Mouse pointer can be moved, but buttons are unresponsive
  • Screen updates stop
  • Hard disk access light stays on (constant)
  • Sometimes continuous beep tone starts

Other clues:
This is fifth attempt at this installation of Vista + CIS (long story, but trying to resolve an issue unrelated to CIS!)
– On first three attempts, no screen freezes were encountered.
– On fourth attempt, Geek Buddy was also installed. Screen freezes were experienced from early on in the Update process, to the extent that the OS installation was abandoned. Research suggested Geek Buddy might be causing the problem.
– On fifth attempt, as described here, now have Geek Buddy unselected at install time. Freezes started very late on in process.

CIS has not requested any user response to alerts, Firewall or otherwise, hence any firewall rules have been generated automatically or are still as default.

The attempts where freezes are encountered have been in the last two days, the others a week or more ago. Is it because of a recent update?

Simple Investigation:
1 - Log-in and start Task Manager as before
2 - Open CIS and disable Firewall for 60 mins
3 - Wait
4 - After 60 mins, Firewall auto-re-enabled
5 - Within 10 mins, screen had frozen.

Have run the checks on hard disk and memory available at power-up: all clear.

Obvious conclusion is that Firewall is causing the freeze, but why?

Help, please?

Having re-read Chiron’s notes, I have UN-selected the Firewall Advanced setting: “Filter Loopback Traffic”.
(The default setting is selected.)

What are the risks associated with leaving this setting disabled?

UPDATE – NOT FIXED:
This appeared to work, for half an hour or so…
…but the freeze still happens, so it’s not the solution.

What causes the freeze?