Hi,
WRITE is used to write values to on chip EEPROM, which the 18F4620 has 1024 bytes of.
You're trying to write to location $4205 which is WAY out of range of the available 1024 bytes.

WRITE 0, step ' <---Will write to the first EEPROM location
WRITE 1023, step '<---Will write to the last EEPROM location

/Henrik.