mm-sources-2.6.2_rc1-r2 fails to fetch the actual mm patchset as it tries to download from the $(OKV) directory (2.6.1) (eg some mirror of http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.1/) but the patch is in fact located in 2.6.2-rc1 directory. As such, the ebuild fails to find the patch.
This seems to be fixed - please run an ``emerge sync'' and then the ebuild should download the patch from the correct path.