[U-Boot] Updating u-boot through tftp

Hi, I'm running u-boot on TI's davinci DM365, I'm trying to update the u-boot from the u-boot, using these commands:

tftp 0x80700000 u-boot-1.3.4_ipnc_dm36x_xxx.bin nand erase 0x2C000 0x20000 nand write 0x80700000 0x2C000 0x20000

but when i try to run the erase command, i'm getting this error:

DM365 EVM :>nand erase 0x2c000 0x20000 NAND erase: device 0 offset 0x2c000, size 0x20000 NAND 256MiB 3,3V 8-bit: MTD Erase failure: -22

How can i do it? is this part locked? Thanks, Alex