[U-Boot] I can not read Linux image from my nand flash

[Peter Pan]

My u-boot version is u-boot-2009-08.
In my U-boot, after I entered "nboot 800000 0 0",
the following messages shows:

Loading from NAND 1GiB 3,3V 8-bit, offset 0x0
   Image Name:   Linux-2.6.22.sac.rd
   Image Type:   PowerPC Linux Kernel Image (gzip compressed)
   Data Size:    1045865 Bytes = 1021.4 kB
   Load Address: 00000000
   Entry Point:  00000000
NAND read from offset ffffffff failed 0
** Read error

The image in nand is written in linux 2.6.22 using
nandwrite -p /dev/mtd3 uImage
This command works fine before.

I looked into the source tree, and u-boot should read out
the first block in my nand flash to show the information
of my image. But, after that, U-boot just think all the following
blocks are bad blocks, so it read failed. But when booting
linux using nfs with linux image in norflash, there is no
bad block shown when linux scan nand for bad blocks. How
could this happen? I have no idea right now.