K770 CID53: Trouble flashing FS with FAR+jdflasher

Hello,

I am trying to upgrade (and eventually unlock) my K770i on the 3 UK network.
See identify log below:

ChipID:9900,EMP protocol:0301
PHONE IS RED RETAIL PRODUCT
FLASH CID detected:53
Speed:921600
Flash ID check:897E
Flash props sent ok
OTP LOCKED:1 CID:51 PAF:1 IMEI:3523840239xxxx CERT:RED
FLASH CID:53 COLOR:RED

Model:K770i
Brand:Sony Ericsson
MAPP CXC article: R8BE001 prg1201-7587_GENERIC_VI
MAPP CXC version: R8BE001
Language Package:HUTCH_1
CDA article: CDA102864/13
CDA version: R6A
Default article: 1201-7603
Default version: R8AB001

Network LOCKED
Operator: MULTIPLE

So, assuming I have read it right and this is a CID53 phone, I have done the following steps so far:
1 - Installed USB driver
2 - Downloaded the files:
K770_R8BE001_MAIN_GENERIC_VI_RED53.mbn
K770_R8BE001_FS_EUROPE_4_RED53.fbn
HB1_06_Gen_CDA102864_13_R6A_GENERIC_EUROPE_4.zip
3 - Checked the mbn and fbn with babeck.exe, both are OK
4 - Connected phone to FAR Manager
5 - Flashed mbn - no problem
6 - Tried to flash fbn, always fails at the same place (block 58 of 149) with this message:
PutFiles(putfile(putfile_flash(flashbabe(get89data (bad89header)))))

To try to fix it I have downloaded and verified about 10 different fbn files (lots of different versions) and they all fail in the same place.
I have also tried flashing with a different copy of FAR Manager, and from a different PC.
I'm running out of things to try, anybody have an idea what could be the reason?

Thanks,
K