[Q] No MBR found after flashing image files into a board

I have a Samsung development board. After flash ICS images files into internal storage, at first time it can boot to android animation but failed to go to launcher; when i boot it again, it report 'NO MBR is found at SD/MMC', and can not be flashed. I use MMC command to create the partition and flash it, same error occurs. u-boot log is:

reading kernel device 0 Start 6144, Count 10240
mmc read 0 0x40008000 6144 10240


MMC read: dev # 0, block # 6144, count 10240 ... there are pending interrupts 0x00000008
error during transfer: 0x00008024
mmc read failed
-1 blocks read: ERROR
completed
reading ramdisk device 0 Start 16384, Count 10240
mmc read 0 0x41000000 16384 10240

MMC read: dev # 0, block # 16384, count 10240 ... there are pending interrupts 0x00000008
[ERROR] response timeout error : 00002104 cmd 18
mmc read failed
-19 blocks read: ERROR
completed