Error de flashtool del Xperia X8: ERR_DYNAMIC="Falló la verificación del encabezado SIN"

Este es el registro de flashtool v0.6.8.0:

17/016/2013 20:16:47 - INFO - <- This level is successfully initialized
17/016/2013 20:16:47 - INFO - Flashtool Version 0.6.8.0 built on 2012-02-26 19:26:25
17/016/2013 20:16:47 - INFO - You can drag and drop ftf files here to start flashing them
17/016/2013 20:16:52 - INFO - Device disconnected
17/016/2013 20:16:55 - INFO - Selected E15_nAa-13_2.6.29.6-nAa-13.ftf
17/016/2013 20:16:55 - INFO - Preparing files for flashing
17/016/2013 20:16:55 - INFO - Please connect your device into flashmode.
17/017/2013 20:17:06 - INFO - Device connected in flash mode
17/017/2013 20:17:06 - INFO - Opening device for R/W
17/017/2013 20:17:07 - INFO - Reading device information
17/017/2013 20:17:07 - INFO - Phone ready for flashmode operations.
17/017/2013 20:17:07 - INFO - Start Flashing
17/017/2013 20:17:07 - INFO - Flashing loader
17/017/2013 20:17:07 - ERROR - ERR_SEVERITY="MAJOR";ERR_CLASS="SECURITY_CLASS";ER R_DYNAMIC="SIN header verification failed" 
17/017/2013 20:17:07 - ERROR - Error flashing. Aborted
17/017/2013 20:17:07 - INFO - Device connected in flash mode
17/017/2013 20:17:08 - INFO - Device disconnected
17/017/2013 20:17:11 - INFO - Device connected in flash mode
17/017/2013 20:17:12 - INFO - Device disconnected

Lo he obtenido de S1TOOL:

Welcome to S1 tool.

TO CONNECT NEXT PHONES
X10 Xperia,E10 Xperia Mini,E15 Xperia X8,U20 Xperia Mini Pro
LT15 Xperia ARC,MT15 Xperia NEO,R800 Xperia PLAY
PRESS AND HOLD "BACK" BUTTON...

PLEASE ATTACH TURNED OFF PHONE NOW

RUNNING S1_EROM VER "R8A029"
SOFTWARE AID: 0001
LOADER AID: 0001
FLASH ID: "0020/00BC"
LOADER VERSION: "R4A045"

MODEL (from GDFS): E15i
SOFTWARE VERSION: 1236-9291_2.1.1.A.0.6
CUSTOM VERSION: 1242-6780_R5B
FILESYSTEM VERSION: WORLD-1-2-5_2.0.1.A.0.47
SERIAL NO: BX902AVHMC

SEMC SIMLOCK CERTIFICATE
Elapsed:10 secs.

¿Por qué no puedo flashear mi Xperia X8? ¿Cómo puedo solucionarlo?