If you are using a OMAP5912 OSK Revision D don’t forget to download the correct U-Boot from here. The file name is osk-u-boot_8_11_05_RevD.bin. It took me quite some time to figure out that this U-Boot version was necessary to boot a 2.6 Kernel on a revision D board. U-Boot’s version should read:
U-Boot 1.1.1 (Aug 4 2005 - 10:41:25)