update log:
Change environment size to match block size.
P.S:
If you are confused by the two images:
"u-boot-hgg420n_hgg420n_128m_ddr3_nand.bin" is for flashing to NAND flash, "u-boot-hgg420n_hgg420n_128m_ddr3_nand.bin" is for uploading to the box via UART cable, it is used with "kwboot" tool, and it is only used for debugging or when you bricked your box.
MD5:
u-boot-hgg420n_hgg420n_128m_ddr3_nand.bin:
a16bfeed7abf88d5cc930ad693cb3b20
u-boot-hgg420n_hgg420n_128m_ddr3_uart.bin:
8bf93837b709f0f8404ffb08689c6723