Root Trouble - Galaxy S II Q&A, Help & Troubleshooting

As in the Orange ICS thread...
Ok, I don't know what I've done.
I've got the Galaxy S2 I9100P on Orange UK.
I was running Gingerbread with TouchWiz as it comes. I had rooted the phone, no bother.
Yesterday, a firmware update became available in Kies. I assumed it would be ICS and so hurriedly installed it. I didn't bother to unroot or anything first. The update was NOT ICS. I can't recall the firmware update details but it screwed up the root access. I knew ICS was coming and so I didn't bother trying to fix it.
Today at work I installed the latest version of Kies on my Windows 7 machine. I checked for updates and ICS was available so I've installed it. No problems.
Now I'm trying to root the phone again. Zerg and SuperOneClick are both reporting problems with the adb driver. Zerg is saying adb server it is out of date, SuperOneClick says it is missing drivers and offers me a forced install. Both attempt to root the phone but fail. Zerg says the following:
Code:
---------------------------------------------------------------
Easy rooting toolkit (v4.0)
created by DooMLoRD
using exploit zergRush (Revolutionary Team)
Credits go to all those involved in making this possible!
---------------------------------------------------------------
[*] This script will:
(1) root ur device using latest zergRush exploit (21 Nov)
(2) install Busybox (1.18.4)
(3) install SU files (binary: 3.0.3 and apk: 3.0.6)
(4) some checks for free space, tmp directory
(will remove Google Maps if required)
[*] Before u begin:
(1) make sure u have installed adb drivers for ur device
(2) enable "USB DEBUGGING"
from (Menu\Settings\Applications\Development)
(3) enable "UNKNOWN SOURCES"
from (Menu\Settings\Applications)
(4) [OPTIONAL] increase screen timeout to 10 minutes
(5) connect USB cable to PHONE and then connect to PC
(6) skip "PC Companion Software" prompt on device
---------------------------------------------------------------
CONFIRM ALL THE ABOVE THEN
Press any key to continue . . .
--- STARTING ----
--- WAITING FOR DEVICE
adb server is out of date. killing...
* daemon started successfully *
--- creating temporary directory
mkdir failed for tmp, File exists
--- cleaning
--- pushing zergRush
1876 KB/s (23060 bytes in 0.012s)
--- correcting permissions
--- executing zergRush
[**] Zerg rush - Android 2.2/2.3 local root
[**] (C) 2011 Revolutionary. All rights reserved.
[**] Parts of code from Gingerbreak, (C) 2010-2011 The Android Exploid Crew.
[-] Not a 2.2/2.3 Android ...
--- WAITING FOR DEVICE TO RECONNECT
if it gets stuck over here for a long time then try:
disconnect usb cable and reconnect it
toggle "USB DEBUGGING" (first disable it then enable it)
--- DEVICE FOUND
--- pushing busybox
3301 KB/s (1075144 bytes in 0.318s)
--- correcting permissions
--- remounting /system
mount: permission denied (are you root?)
--- checking free space on /system
142 KB/s (439 bytes in 0.003s)
df: /mnt/.lfs: Function not implemented
df: /mnt/secure/asec: Permission denied
--- Free space on /system : 5176 bytes
--- NOT enough free space on /system!!!
--- making free space by removing Google Maps
--- copying busybox to /system/xbin/
/system/xbin/busybox: cannot open for write: Read-only file system
--- correcting ownership
Unable to chmod /system/xbin/busybox: No such file or directory
--- correcting permissions
Unable to chmod /system/xbin/busybox: No such file or directory
--- installing busybox
/system/bin/sh: /system/xbin/busybox: not found
--- pushing SU binary
failed to copy 'files\su' to '/system/bin/su': Read-only file system
--- correcting ownership
Unable to chmod /system/bin/su: No such file or directory
--- correcting permissions
Unable to chmod /system/bin/su: No such file or directory
--- correcting symlinks
rm failed for /system/xbin/su, No such file or directory
link failed Read-only file system
--- pushing Superuser app
failed to copy 'files\Superuser.apk' to '/system/app/./Superuser.apk': Read-only
file system
--- cleaning
--- rebooting
ALL DONE!!!
Press any key to continue . . .
I don't know where the problem lies exactly or how to fix it.
Any hints? Is it a driver issue? Was it the update I ran before without unrooting? Is this a known issue? Am I doing something dumb?
Cheers.