Felix,

(With apologies to T-U readers as this has become somewhat O/T but
I hope it is still useful.)

The linux-image install may be failing as a result of a config
file left over from a removed but not purged package or an
obsolete config file resulting from a downgrade or failed upgrade.

Try the following (all on one line):

dpkg-query --show --showformat='${STATUS} ${PACKAGE} ${VERSION} 
${ARCHITECTURE}\n' | grep 'deinstall ok config-files' | awk '{print $4}'

That should give you a list of packages to be purged.  If it
looks OK add a "dpkg --purge $(" on the front and a ")" on the
end to purge them.

Then try the reinstall again.  If it works great.  If it fails
please show me the result of:

  grep 'obsolete$' /var/lib/dpkg/status

--Mike