Your problem probably arises from toolchains incompatibility. You are using a toolchain different from the one used for compiling all the rest of the distribution you are updating the kernel to.
If you are using Angstrom, U-boot was compiled with one of official Angstrom toolchain while your kernel was compiled against the toolchain provided by codesourcery.
Pls consider to switch to an official Angstrom toolchain, http://www.angstrom-distribution.org/toolchains/
Best Regards