[XPERIA X10 Q&A, Help & Troubleshooting] Dr Goodvibes:
OP sorry, I have no answers, but I have the same/similar problem.

I figure if I add my information to the information you have provided we may collectively invite some comment to stair us in the direction to an answer.

OP, hope that's OK with you. :)

Just one thing OP, have you installed the Flashtool 0.9.9 Windows update/bug fix (assuming you're using windows)??

FlashTool-windows-0.9.9update1.zip

I am having all sorts of problems attempting to install a CM9/CM10 kernel with CWM recovery mode on my XPERIA X10i.

My end goal is to install [CM10] v4 (Torch) by: scritch007

I have an unlock??? bootloader and can root my phone. But I'm beginning to question that!!!

I have the following information provided from S1 Tool

Welcome to S1 tool.

RUNNING S1_EROM VER "R8A031"
SOFTWARE AID: 0001
LOADER AID: 0001
FLASH ID: "002C/00B3"
LOADER VERSION: "R4A024"

MODEL (from GDFS): X10i
SOFTWARE VERSION: 1227-4612_3.0.1.G.0.75
CUSTOM VERSION: 1241-1846_R1C
FILESYSTEM VERSION: WORLD-1-4-8_3.0.1.G.0.75
SERIAL NO: CB537QU1MN

SEMC SIMLOCK CERTIFICATE
Elapsed:55 secs.

Using the service information menu *#*#7378423#*#* I was able to see my SIM lock was unlocked [] SIM = 0

I have installed a fresh copy of GB 2.3.3 using Flashtool 0.9.9 with additional Windows update1.

I used a 'World' GB 2.3.3 ftf see above.

I have also installed GB using Sony Ericsson Update Service (SEUS) which provides the same base OS.

[Root XPERIA X10i using FlashTool 0.9.9]

I have rooted the device using ZergRush exploit from Flashtools 0.9.9 with update patch FlashTool-windows-0.9.9update1.zip

To do this, I started the phone and enabled debug and unknown source.

With the phone still up and running and Flashtool 0.9.9 also running, I plugged in the USB cable.

I select the "My X10" option -> root -> Force ZergRush and the process then rooted the phone and the phone rebooted with root access, no problems there.

19/042/2012 11:42:06 - INFO - <- This level is successfully initialized
19/042/2012 11:42:06 - INFO - Flashtool Version 0.9.9.0 built on 2012-11-21 23:15:59
19/042/2012 11:42:06 - INFO - You can drag and drop ftf files here to start flashing them
19/042/2012 11:42:12 - INFO - Device connected with USB debugging on
19/042/2012 11:42:12 - INFO - Connected device : X10
19/042/2012 11:42:12 - INFO - Installed version of busybox : BusyBox v1.15.3 (2010-02-06 17:13:19 CET) multi-call binary
19/042/2012 11:42:12 - INFO - Android version : 2.3.3 / kernel version : 2.6.29-modFXP-DooMKernel-v06 / Build number : 3.0.1.G.0.75
19/042/2012 11:42:12 - INFO - Root Access Allowed

I can also install CWM recovery this way too.

After I have gained root access I have the phone up and running and again plug the USB cable in.

I select recovery mode option in Flashtool 0.9.9 and I'm requested to power down my phone and reconnect.

This then installs a recovery mode, either CWM or xRecovery depending on which one I select.

Again, this is all good and I can boot into either xRecovery or CWM recovery depending on which is installed.

I have installed and used other versions of Flashtool, however the outcomes always seems to be the same.

If I attempt to install a CM9/CM10 ftf I get the following error message:

19/016/2012 03:16:36 - INFO - <- This level is successfully initialized
19/016/2012 03:16:36 - INFO - Flashtool Version 0.9.9.0 built on 2012-11-21 23:15:59
19/016/2012 03:16:36 - INFO - You can drag and drop ftf files here to start flashing them
19/016/2012 03:16:42 - INFO - Device disconnected
19/016/2012 03:16:55 - INFO - Selected X10_4.1.X_CMX10_bootmanager_v14.ftf
19/016/2012 03:16:55 - INFO - Preparing files for flashing
19/016/2012 03:16:56 - INFO - Please connect your device into flashmode.
19/017/2012 03:17:45 - INFO - Device connected in flash mode
19/017/2012 03:17:46 - INFO - Opening device for R/W
19/017/2012 03:17:46 - INFO - Reading device information
19/017/2012 03:17:46 - INFO - Phone ready for flashmode operations.
19/017/2012 03:17:46 - INFO - Start Flashing
19/017/2012 03:17:46 - INFO - Processing loader
19/017/2012 03:17:46 - INFO - Checking header
19/017/2012 03:17:46 - INFO - Ending flash session
19/017/2012 03:17:46 - ERROR - ERR_SEVERITY="MAJOR";ERR_CLASS="SECURITY_CLASS";ERR_DYNAMIC="SIN header verification failed"
19/017/2012 03:17:46 - ERROR - Error flashing. Aborted
19/017/2012 03:17:46 - INFO - Device connected in flash mode
19/017/2012 03:17:47 - INFO - Device disconnected
19/017/2012 03:17:49 - INFO - Device connected in flash mode
19/018/2012 03:18:10 - INFO - Device disconnected
19/018/2012 03:18:13 - INFO - Device connected with USB debugging off
19/018/2012 03:18:13 - INFO - For 2011 devices line, be sure you are not in MTP mode
19/018/2012 03:18:23 - INFO - Device disconnected

At the moment I have just given up until I have some good leads to renew my CM9/CM10 install efforts.

At the moment I have GB 2.3.3 rooted with ZergRush exploit.

xRecovery installed

DooMLoRD DooMkernel V6 install with overclocked CPU of 1152MHz

The phone is up and running, rooted and has a modified Kernel which I recovered via xRecovery backup restore.

So, I have a working GB 2.3.3 phone with root access....but I want more...:)

My phone seems to be a one trick pony and I don't seem to be able to install CM9/CM10 with the information I have to hand.

Any thoughts I why I'd be getting the "SIN header verification failed" message????

********* Update **************

[ANSWER]

I solved my problem by unlocking the bootloader on my XPERIA X10i using the following information.

Tutorial: Rooting, Bootloader unlocking&updating

Remember to have debugging and Unknown source ticked on your XPERIA X10i phone.

20/015/2012 16:15:44 - INFO - Device connected with USB debugging off
20/015/2012 16:15:44 - INFO - For 2011 devices line, be sure you are not in MTP mode
20/015/2012 16:15:44 - INFO - Device connected with USB debugging on
20/015/2012 16:15:45 - INFO - Connected device : X10
20/015/2012 16:15:45 - INFO - Installed version of busybox : BusyBox v1.19.0 (2011-08-14 23:46:58 CDT) multi-call binary.
20/015/2012 16:15:45 - INFO - Android version : 2.3.3 / kernel version : 2.6.29-00054-g5f01537
20/015/2012 16:15:46 - INFO - Remounting system read-write
20/015/2012 16:15:46 - INFO - Installing toolbox to device...
20/015/2012 16:15:46 - INFO - Pushing C:\Program Files\Flashtools 0.8.6\Flashtool\custom\root\ftkit.tar to /data/local/tmp
20/015/2012 16:15:46 - INFO - Running installftkit as root thru sysrun
20/015/2012 16:15:47 - INFO - Root Access Allowed
20/016/2012 16:16:22 - INFO - Please connect your device into flashmode.
20/016/2012 16:16:27 - INFO - Device disconnected
20/017/2012 16:17:22 - INFO - Device connected in flash mode
20/017/2012 16:17:22 - INFO - Opening device for R/W
20/017/2012 16:17:22 - INFO - Reading device information
20/017/2012 16:17:22 - INFO - Phone ready for flashmode operations.
20/017/2012 16:17:22 - INFO - Flashing loader
[COLOR="Red"]20/017/2012 16:17:24 - INFO - Loader : S1_Loader_Root_f851 - Version : R4A024 / Bootloader status : UNROOTABLE[/COLOR]
20/017/2012 16:17:24 - INFO - Start Reading property
20/017/2012 16:17:24 - INFO - Reading TA finished.
20/017/2012 16:17:24 - INFO - Ending flash session
20/017/2012 16:17:24 - INFO - Found semcSL
20/017/2012 16:17:24 - INFO - You can now unplug and turn on device, then plug it again
20/017/2012 16:17:24 - INFO - Waiting for device
20/019/2012 16:19:39 - INFO - Device connected with USB debugging on
20/019/2012 16:19:40 - INFO - Pushing C:\Program Files\Flashtools 0.8.6\Flashtool\custom\features\UnlockBL\files\qsd8250\qsd8250bootwrite_semcSL to /data/local/tmp
20/019/2012 16:19:40 - INFO - Pushing C:\Program Files\Flashtools 0.8.6\Flashtool\custom\features\UnlockBL\files\qsd8250\mapper_2.6.29-00054-g5f01537.ko to /data/local/tmp
20/019/2012 16:19:40 - INFO - Pushing C:\Program Files\Flashtools 0.8.6\Flashtool\custom\features\UnlockBL\files\qsd8250\fixPart to /data/local/tmp
20/019/2012 16:19:40 - INFO - Running runfixPart as root thru sysrun
20/019/2012 16:19:41 - INFO - Successfully applied fixPart. Rebooting
20/019/2012 16:19:41 - INFO - Waiting for device
20/019/2012 16:19:42 - INFO - Device disconnected
20/019/2012 16:19:53 - INFO - Device connected with USB debugging off
20/019/2012 16:19:53 - INFO - For 2011 devices line, be sure you are not in MTP mode
20/019/2012 16:19:57 - INFO - Device connected with USB debugging on
20/020/2012 16:20:10 - INFO - Running runbootwrite as root thru sysrun
20/020/2012 16:20:11 - INFO - Successfully applied unlock. Rebooting
20/020/2012 16:20:11 - INFO - Running runClean as root thru sysrun
20/020/2012 16:20:13 - INFO - Device disconnected
20/020/2012 16:20:24 - INFO - Device connected with USB debugging off
20/020/2012 16:20:24 - INFO - For 2011 devices line, be sure you are not in MTP mode
20/020/2012 16:20:33 - INFO - Device disconnected
20/020/2012 16:20:36 - INFO - Device connected with USB debugging on
20/020/2012 16:20:36 - INFO - Connected device : X10
20/020/2012 16:20:36 - INFO - Installed version of busybox : BusyBox v1.19.0 (2011-08-14 23:46:58 CDT) multi-call binary.
20/020/2012 16:20:36 - INFO - Android version : 2.3.3 / kernel version : 2.6.29-00054-g5f01537
20/020/2012 16:20:48 - INFO - Root Access Allowed
20/023/2012 16:23:12 - INFO - Device disconnected
20/024/2012 16:24:10 - INFO - Log written to C:\Program Files\Flashtools 0.8.6\Flashtool\flashtool_2012-12-19_04-10-47.log

Don't 'freak out' when you see "Bootloader status : UNROOTABLE" scroll across the screen. My heart sunk when I saw that, but I let the first phase of the process complete and then connect the phone to the USB cable after the phone had re-booted with Flashtool 0.8.6 (in my case) still running and the process completed. In my case I got my phone back unlocked and still rooted. All good.

I'm pretty sure my bootloader was not locked when I started out a year or so ago, but I can't be absolutely sure; so somehow it's seems to have become locked during that time. Maybe because I was just recovering the same build each time I never installed anything else to check.

Like the OP, I originally rooted my phone by using 0.2.9.1 GB-ready using a convoluted process compared to todays one click root process.

Now when I flash a ftf file in Flashtool it runs through without any errors.

I was then able to go on and install [CM10] v4 (Torch) by: scritch007 without any problems.

Hope some of this information can help others.