[Xperia SP Q&A, Help & Troubleshooting] rexxxxx:
tried to do just that - but when try to flash stock firmware I get this:

23/034/2015 18:34:12 - INFO - Selected Bundle for Sony Xperia SP (C5303). FW release : 12.0.A.1.257. Customization : Customized_NCB

23/034/2015 18:34:12 - INFO - Preparing files for flashing

23/034/2015 18:34:24 - INFO - Please connect your device into flashmode.

23/034/2015 18:34:33 - INFO - Device connected in flash mode

23/034/2015 18:34:34 - INFO - Opening device for R/W

23/034/2015 18:34:34 - INFO - Reading device information

23/034/2015 18:34:34 - INFO - Phone ready for flashmode operations.

23/034/2015 18:34:34 - INFO - Opening TA partition 2

23/034/2015 18:34:34 - INFO - Current device : C5303 - CB51243CRJ - 1272-3352_R1B - 1272-3352_12.1.A.1.207 - GLOBAL-LTE_12.1.A.1.207

23/034/2015 18:34:34 - INFO - Closing TA partition

23/034/2015 18:34:34 - INFO - Start Flashing

23/034/2015 18:34:34 - INFO - Processing loader.sin

23/034/2015 18:34:34 - INFO - Checking header

23/034/2015 18:34:34 - INFO - Flashing data

23/034/2015 18:34:39 - INFO - Loader : S1_Root_7054 - Version : R5G006 / Boot version : R11B023 / Bootloader status : NOT_ROOTABLE

23/034/2015 18:34:39 - INFO - Max packet size set to 64K

23/034/2015 18:34:39 - INFO - Making a TA backup

23/034/2015 18:34:39 - INFO - Opening TA partition 1

23/034/2015 18:34:39 - INFO - Start Dumping TA partition 1

23/034/2015 18:34:43 - INFO - Finished Dumping TA partition 1

23/034/2015 18:34:43 - INFO - TA partition 1 saved to C:\Users\radi\.flashTool\registeredDevices\CB51243CRJ\s1ta\2015-09-23_06-34-39\1.ta

23/034/2015 18:34:43 - INFO - Closing TA partition

23/034/2015 18:34:43 - INFO - Opening TA partition 2

23/034/2015 18:34:43 - INFO - Start Dumping TA partition 2

23/034/2015 18:34:44 - INFO - Finished Dumping TA partition 2

23/034/2015 18:34:44 - INFO - TA partition 2 saved to C:\Users\radi\.flashTool\registeredDevices\CB51243CRJ\s1ta\2015-09-23_06-34-39\2.ta

23/034/2015 18:34:44 - INFO - Closing TA partition

23/034/2015 18:34:44 - INFO - No flash script found. Using 0.9.18 flash engine

23/034/2015 18:34:44 - INFO - Disabling final data verification check

23/034/2015 18:34:44 - INFO - Disabling final verification

23/034/2015 18:34:44 - INFO - Opening TA partition 2

23/034/2015 18:34:44 - INFO - Writing TA unit 00002774. Value : [01]

23/034/2015 18:34:44 - INFO - Closing TA partition

23/034/2015 18:34:44 - INFO - Processing partition-image.sin

23/034/2015 18:34:44 - INFO - Checking header

23/034/2015 18:34:44 - INFO - Flashing data

23/034/2015 18:34:44 - INFO - Opening TA partition 2

23/034/2015 18:34:45 - INFO - Closing TA partition

23/034/2015 18:34:45 - INFO - Opening TA partition 2

23/034/2015 18:34:45 - INFO - Processing amss_fsg.sin

23/034/2015 18:34:45 - INFO - Checking header

23/034/2015 18:34:45 - INFO - Flashing data

23/034/2015 18:34:45 - INFO - Processing amss_fs_1.sin

23/034/2015 18:34:45 - INFO - Checking header

23/034/2015 18:34:45 - INFO - Flashing data

23/034/2015 18:34:45 - INFO - Processing amss_fs_2.sin

23/034/2015 18:34:45 - INFO - Checking header

23/034/2015 18:34:45 - INFO - Flashing data

23/034/2015 18:34:45 - INFO - Processing apps_log.sin

23/034/2015 18:34:45 - INFO - Checking header

23/034/2015 18:34:45 - INFO - Flashing data

23/034/2015 18:34:45 - INFO - Processing cache.sin

23/034/2015 18:34:45 - INFO - Checking header

23/034/2015 18:34:46 - INFO - Flashing data

23/034/2015 18:34:47 - INFO - Processing fotakernel.sin

23/034/2015 18:34:47 - INFO - Checking header

23/034/2015 18:34:47 - INFO - Flashing data

23/034/2015 18:34:48 - INFO - Processing kernel.sin

23/034/2015 18:34:48 - INFO - Checking header

23/034/2015 18:34:48 - INFO - Flashing data

23/034/2015 18:34:50 - INFO - Closing TA partition

23/034/2015 18:34:50 - INFO - Opening TA partition 2

23/034/2015 18:34:50 - INFO - Processing system.sin

23/034/2015 18:34:50 - INFO - Checking header

23/034/2015 18:34:51 - ERROR - Processing of system.sin finished with errors.

23/034/2015 18:34:51 - INFO - Ending flash session

23/034/2015 18:34:51 - ERROR -

23/034/2015 18:34:51 - ERROR - Error flashing. Aborted

23/034/2015 18:34:51 - INFO - Flashing finished.

23/034/2015 18:34:51 - INFO - Please unplug and start your phone

23/034/2015 18:34:51 - INFO - For flashtool, Unknown Sources and Debugging must be checked in phone settings

23/034/2015 18:34:51 - INFO - Device connected in flash mode

23/034/2015 18:34:52 - INFO - Device disconnected

23/034/2015 18:34:55 - INFO - Device connected in flash mode

23/035/2015 18:35:13 - INFO - Device disconnected

any idea what is wrong ?

BTW it appears as it have flashed something as I am unable to boot anymore - custom recovery is also not accessible.

any help will be appreciated

thanks