Hello,
I have started a clean build on 2.6.26.8 by following this instruction.
http://www.henrynestler.com/colinux/testing/kernel-2.6.26.8/
This the failure I got. Seems some patch is missing for unionfs, base on this thread,
http://kerneltrap.org/mailarchive/linux-kernel/2007/10/21/349924/thread

---------------------------------- error log ------------------------------
Making Kernel 2.6.26.8
Making Modules 2.6.26.8

  --- BUILD LOG /mnt/hda/log/build-colinux-31633.log:
make[1]: Entering directory `/mnt/hda/build/linux-2.6.26.8-build'
make -C /mnt/hda/build/linux-2.6.26.8-source O=/mnt/hda/build/linux-2.6.26.8-build/. vmlinux
  Using /mnt/hda/build/linux-2.6.26.8-source as source for kernel
  GEN     /mnt/hda/build/linux-2.6.26.8-build/Makefile
  CHK     include/linux/version.h
  CHK     include/linux/utsrelease.h
  CALL    /mnt/hda/build/linux-2.6.26.8-source/scripts/checksyscalls.sh
  CHK     include/linux/compile.h
make[1]: Leaving directory `/mnt/hda/build/linux-2.6.26.8-build'
make[1]: Entering directory `/mnt/hda/build/linux-2.6.26.8-build'
make -C /mnt/hda/build/linux-2.6.26.8-source O=/mnt/hda/build/linux-2.6.26.8-build/. modules modules_install
  Using /mnt/hda/build/linux-2.6.26.8-source as source for kernel
  GEN     /mnt/hda/build/linux-2.6.26.8-build/Makefile
  CHK     include/linux/version.h
  CHK     include/linux/utsrelease.h
  CALL    /mnt/hda/build/linux-2.6.26.8-source/scripts/checksyscalls.sh
  CHK     include/linux/compile.h
  Building modules, stage 2.
  MODPOST 294 modules
make[1]: Leaving directory `/mnt/hda/build/linux-2.6.26.8-build'

  --- ERROR LOG /mnt/hda/log/build-colinux-31633.err:
ERROR: "security_inode_permission" [fs/unionfs/unionfs.ko] undefined!
make[4]: *** [__modpost] Error 1
make[3]: *** [modules] Error 2
make[2]: *** [sub-make] Error 2
make[1]: *** [all] Error 2
Kernel 2.6.26.8 make modules failed
make: *** [kernel] Error 1