OK, so problem probably isn't to build the image, but to flash it properly. That's another thing.
1. follow instructions in START User's Guide from Linux documentation package to program bootloader (located in rootfs/boot/ folder of your LTIB build) to SD card. This is quite simple and should always boot.
2. try to start the bootloader from SD card. Does it show anything on serial port? If yes, go step 3, otherwise back to step 1 :-)
3. Follow instructions in user's guide to program kernel image.
4. Boot into uboot, interrupt the boot process and set up boot parameters according to user's guide. Save boot parameters and reboot. Does kernel start to execute after uboot? If yes then 5...
5. Set up file system parameters to kernel (either through NFS or format SD card and set params accordingly...)
One step at a time and you can get this to work quite easily...