Reading places that firmware can be flashed with bootcodes 16 and 18 and not sure what one you have?
To check which bootcode version is installed, press Stop then Pause button @ HOME screen
You will see something like from this example
System rev P0020BC18-61
Bootup 27
Bootcode 0000.0202.0027
Here is the breakdown.
System rev P0020BC18-61
Firmware version is P61
System rev P0020BC18-61
For BC18+ devices
Bootcode 0000.0202.0027
bootcode is 27.
What does this all mean?
BootCode 18 mean BC18 and above. You can also flash any BC16 firmware.
As long as you have 18 and above anything goes.
So 27 is above 18 and anything goes
Note that BC18+ firmwares wont remount as read/write, you need a BC16+ firmware to do that.
Source http://www.patriotmem.com/forums/showthread.php?t=5363