kernel boot problem

We have a problem in booting kernel.The board has preloaded boot files
on the NAND. So, when we boot it from NAND , it works fine. But, when
we boot the board from a SD card, it doesn't work.
The booting stops after uboot at 'starting kernel...'

Do not know what went wrong. The instructions in the manual for
partitioning SD card and loading the files are properly followed.

We tried loading some demo files thinking there would be some mistake
in the compilation of the files. But even demo did not work.

Please help to find what went wrong.

since it works fine on NAND there may not be any problem in the files
u used.. so the problem may be due to
mmc card u used or the uImage may be corrupted while u copy in to
card... when u-boot finishes fine the mmc card no more needed(uImage
will be in ram)..