[Motorola Atrix HD] eagleeyetom:
Maybe you should try to use method provided by DooMLoRD to unlock Xperia Arc?

@echo ---------------------------------------------------------------
@echo	Xperia 2011 ICS Easy Rooting toolkit (v1.0)
@echo created by DooMLoRD
@echo "andorid emulator" trick
@echo Credits go to all those involved in making this possible!
@echo ---------------------------------------------------------------
@echo [*] This script will:
@echo (1) root ur device using "andorid emulator" trick
@echo (2) install Busybox (1.18.4)
@echo (3) install SU files (ICS specific)
@echo (4) do some checks for free space, tmp directory
@echo (will remove Google Maps if required)
@echo [*] Before u begin:
@echo (1) make sure u have installed adb drivers for ur device
@echo (2) enable "USB DEBUGGING"
@echo from (Menu\Settings\Developer Options\Development)
@echo (3) enable "UNKNOWN SOURCES"
@echo from (Menu\Settings\Security)
@echo (4) [OPTIONAL] increase screen timeout to 10 minutes
@echo (5) connect USB cable to PHONE and then connect to PC
@echo (6) skip "PC Companion Software" prompt on device
@echo ---------------------------------------------------------------
@echo CONFIRM ALL THE ABOVE THEN
@pause
@echo --- STARTING ----
@echo --- WAITING FOR DEVICE
@files\adb wait-for-device
@echo --- creating temporary directory
@files\adb shell "cd /data/local && mkdir tmp"
@echo --- cleaning
@files\adb shell "cd /data/local/tmp/ && rm *"
@echo --- symlinking tmp directory
@files\adb shell mv /data/local/tmp /data/local/tmp.bak
@files\adb shell ln -s /data /data/local/tmp
@echo --- Rebooting
@files\adb reboot
@echo --- WAITING FOR DEVICE TO RECONNECT
@echo --- PLEASE WAIT, THIS MAY TAKE A WHILE
@echo if it gets stuck over here for a long time then try:
@echo disconnect usb cable and reconnect it
@echo toggle "USB DEBUGGING" (first disable it then enable it)
@files\adb wait-for-device
@echo --- DEVICE FOUND
@echo --- enabling emulator hack
@files\adb shell rm /data/local.prop > nul
@files\adb shell "echo \"ro.kernel.qemu=1\" > /data/local.prop"
@echo --- Rebooting
@files\adb reboot
@echo --- WAITING FOR DEVICE TO RECONNECT
@echo --- PLEASE WAIT, THIS MAY TAKE A WHILE
@echo if it gets stuck over here for a long time then try:
@echo disconnect usb cable and reconnect it
@echo toggle "USB DEBUGGING" (first disable it then enable it)
@files\adb wait-for-device
@echo --- DEVICE FOUND
@echo --- pushing busybox
@files\adb push files\busybox /data/local/tmp/.
@echo --- correcting permissions
@files\adb shell "chmod 755 /data/local/tmp/busybox"
@echo --- remounting /system
@files\adb shell "/data/local/tmp/busybox mount -o remount,rw /system"
@echo --- checking free space on /system
@files\adb push files\makespace /data/local/tmp/.
@files\adb shell "chmod 777 /data/local/tmp/makespace"
@files\adb shell "./data/local/tmp/makespace"
@echo --- copying busybox to /system/xbin/
@files\adb shell "dd if=/data/local/tmp/busybox of=/system/xbin/busybox"
@echo --- correcting ownership
@files\adb shell "chown root.shell /system/xbin/busybox"
@echo --- correcting permissions
@files\adb shell "chmod 04755 /system/xbin/busybox"
@echo --- installing busybox
@files\adb shell "/system/xbin/busybox --install -s /system/xbin"
@files\adb shell "rm -r /data/local/tmp/busybox"
@echo --- pushing SU binary
@files\adb push files\su /system/bin/su
@echo --- correcting ownership
@files\adb shell "chown root.shell /system/bin/su"
@echo --- correcting permissions
@files\adb shell "chmod 06755 /system/bin/su"
@echo --- correcting symlinks
@files\adb shell "rm /system/xbin/su"
@files\adb shell "ln -s /system/bin/su /system/xbin/su"
@echo --- pushing Superuser app
@files\adb push files\Superuser.apk /system/app/.
@echo --- cleaning
@files\adb shell rm /data/local.prop
@files\adb shell rm /data/local/tmp
@files\adb shell mv /data/local/tmp.bak /data/local/tmp
@echo --- rebooting
@files\adb reboot
@echo ALL DONE!!!
@pause