[U-Boot] Swiching u-boot image in SPI-NOR

Hello I am trying to bring in u-boot.imx (uboot image of u-boot 2013) onto SPI-NOR of nitrogen 6x board.I used following commands:

...

sf probe 1 sf erase 0 0x40000 fatload mmc 0:1 12000000 u-boot.imx

reading u-boot.imx 343040 bytes read in 54 ms (6.1 MiB/s)

...

sf write 0x12000000 0x0 343040

ERROR: attempting write past flash size (0x200000)

I have no clue as how to overcome this error.Can somebody help me with this error.

Thanks in Advance!