U-BOOT环境变量保存问题

突然间发现了这个问题，保存了环境变量后还是有*** Warning - bad CRC or NAND, using default environment，
这是为什么呢？该怎么解决啊，U-BOOT根本就没有改过！
U-Boot 1.3.4 (Nov 16 2012 - 16:52:39)
DRAM:  64 MB
Flash:  2 MB
NAND:  256 MiB
*** Warning - bad CRC or NAND, using default environment
In:    serial
Out:   serial
Err:   serial
dm9000 i/o: 0x20000300, id: 0x90000a46
DM9000: running in 16 bit mode
MAC: 08:00:3e:26:0a:5b
operating at unknown: 0 mode
Hit any key to stop autoboot:  0
ARM2440 # saveenv
Saving Environment to NAND...
Erasing Nand...
Erasing at 0x40000 -- 100% complete.
Writing to Nand... done
?M2440 # reset
U-Boot 1.3.4 (Nov 16 2012 - 16:52:39)
DRAM:  64 MB
Flash:  2 MB
NAND:  256 MiB
*** Warning - bad CRC or NAND, using default environment
In:    serial
Out:   serial
Err:   serial
dm9000 i/o: 0x20000300, id: 0x90000a46
DM9000: running in 16 bit mode
MAC: 08:00:3e:26:0a:5b
operating at unknown: 0 mode
Hit any key to stop autoboot:  0
ARM2440 #