Newbie: create arm linux kernel image problem, please help

I've been a user of armboot about 4 months, since it's replaced by
u-boot, I try to use u-boot instead of armboot. But I cann't create a bootable uImage now, the error is:

    (my kernel is arm-linux-2.4.19-rmk7-pxa1, my platform is lubbock-pxa250)
I create uImage like:
    make lubbock_config
    make oldconfig
    make dep
    make zImage
    mkimage -A arm -O linux -C none -T kernel -a 0xa0008000 -e 0xa0008000 -n
"uImage" -d zImage uImage
then start u-boot:
    erase 1:1-4
    loadb 0xa0008000(send uImage)
    cp.b 0xa0008000 0x40000 0x100000
    bootm 0x40000

then I got the error like:
...
Starting kernel ...
Uncompressing Linux........(prefetch abort or hangs)

if I create uImage like:
arm-linux-objcopy -O binary -R .note -R .comment -S vmlinux linux.bin gzip -9 linux.bin
mkimage -A arm -O linux -C gzip -T kernel -a 0xa0008000 -e 0xa0008000 -n
"uImage" -d linux.bin.gz uImage
then I got the error like:

    ...
    Starting kernel ...
    (hangs)

what should I do, please help.
Hongda Zhao