This will fix your unlocked Phones which got bricked through OTA update and are dead now!
Please download this package:
MOD EDIT Link Removed at OPs request
Let it extract to a destination of your choice.
After that run Flashtool.exe.
Now hit the button FLASH and select the package which is included.
Follow the steps and connect your phone in flashmode. This is the same mode Pc Companion and SEUS uses to flash your phone to newer firmare (Indicated by green LED), if you got BLUE LED you are in the wrong mode!
Flashtool will now detect your phone and start the repair.
After all is done your phone should be up and running again.
PLEASE DO NOT ACCEPT ANY OTA'S ! If you receive a OTA message just decline, if you accept it you will end with a brick AGAIN! So please do NOT accept them until SonyEricsson provides a OTA solution for unlocked Bootloaders!