Hi,
in order to be able to perform serial boot, you need to know the password that is stored in shadow flash memory at address 0x00FF_FDD8 - 0x00FF_FDDF. It is necessary to use the password in BAM protocol even if the device is not censored - we have to use default password 0xFEED_FACE_CAFE_BEEF in this case.
Here are important passages from reference manual:


Also take a look at this application note:
http://www.freescale.com/files/microcontrollers/doc/app_note/AN4674.pdf
Regards,
Lukas