uImage to sdcard

Hi

I have been following the instructions on this site http://elinux.org/Building_BBB_Kernel to create a new kernel, and it boots over tftp as the instructions show. I am having trouble getting the new uImage onto an sdcard with u-boot. I have tried swapping the uImage with the existing one on the eMMC but this does not work. Has anyone got this working?

Thanks in advance

Steve