[yocto] [Intel Edison] Changing kernel configuration results in "do_rootfs"-failure (Code 255)

[yocto yocto]

I tried to add a module to the kernel configuration according to

http://www.yoctoproject.org/docs/1.6.1/kernel-dev/kernel-dev.html#changing-the-configuration

Here is what I have done:

File:
meta-mylayer/recipes-kernel/linux/linux-yocto_3.10.bbappend

Contains:
FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
SRC_URI += "file://FTDI.cfg"

File:
meta-mylayer/recipes-kernel/linux/files/FTDI.cfg

Contains:
CONFIG_USB_SERIAL=y
CONFIG_USB_SERIAL_FTDI_SIO=y

File:
meta-mylayer/recipes-mylayer/images/mylayer-image.bb

Contains:
IMAGE_INSTALL += " \
    linux-yocto \
    [...]


Bitbake result:
ERROR: Unable to install packages. Command
'/home/ubuntu/development/edison-src/build/tmp/sysroots/x86_64-linux/usr/bin/opkg-cl
-f
/home/ubuntu/development/edison-src/build/tmp/work/edison-poky-linux/geent-image/1.0-r0/opkg.conf
-o
/home/ubuntu/development/edison-src/build/tmp/work/edison-poky-linux/geent-image/1.0-r0/rootfs
--force_postinstall --prefer-arch-to-version   install i2c-tools
run-postinsts nano useradd linux-yocto base-files postgresql
packagegroup-core-boot' returned 255:
[...]
Collected errors:
 * opkg_install_cmd: Cannot install package linux-yocto.
[...]
ERROR: Function failed: do_rootfs


What might be wrong here?
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