dpkg --unpack: unable to create /usr/lib/dpkg/mksplit.dpkg-new

I was updating some lucid boxes (apt-get update; apt-get upgrade).

# lsb_release -rd
Description: Ubuntu 10.04.4 LTS
Release: 10.04

In one of them things worked like a charm.

But in another one the upgrading failed because of not being able to write to /var/cache/apt/archives/partial/ or similar; it looks like not downloading the new packages because of not being able to write them to disk.

Executing "apt-get clean" solved this problem, but then the upgrade fails because it cannot create /usr/lib/dpkg/mksplit.dpkg-new

-- 8< --

Extrayendo plantillas para los paquetes: 100%
Preconfigurando paquetes ...
(Leyendo la base de datos ... 00%
23767 ficheros y directorios instalados actualmente.)
Preparando para reemplazar dpkg 1.15.5.6ubuntu4.5 (usando .../dpkg_1.15.5.6ubuntu4.6_amd64.deb) ...
Desempaquetando el reemplazo de dpkg ...
dpkg: error al procesar /var/cache/apt/archives/dpkg_1.15.5.6ubuntu4.6_amd64.deb (--unpack):
 unable to create `/usr/lib/dpkg/mksplit.dpkg-new' (while processing `./usr/lib/dpkg/mksplit'): Invalid argument
dpkg-deb: el subproceso paste fue terminado por la señal (Broken pipe)
Se encontraron errores al procesar:
 /var/cache/apt/archives/dpkg_1.15.5.6ubuntu4.6_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

-- 8< -- My translation of the error message:

Extracting templates for the packages: 100%
Preconfiguring packages
(Reading data base ... 00%
23767 archives and directories currently installed.)
Preparing to replace dpkg 1.15.5.6ubuntu4.5 (using .../dpkg_1.15.5.6ubuntu4.6_amd64.deb) ...
Unpacking the replacement of dpkg ...
dpkg: error processing /var/cache/apt/archives/dpkg_1.15.5.6ubuntu4.6_amd64.deb (--install):
 unable to create `/usr/lib/dpkg/mksplit.dpkg-new' (while processing `./usr/lib/dpkg/mksplit'): Invalid argument
dpkg-deb: the subprocess paste was terminated by the signal (Broken pipe)
There were errors processing:
 /var/cache/apt/archives/dpkg_1.15.5.6ubuntu4.6_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

-- >8 --

Trying "dpkg -i /var/cache/apt/archives/dpkg_1.15.5.6ubuntu4.6_amd64.deb" produces the same error:

-- 8< --

(Leyendo la base de datos ... 00%
23767 ficheros y directorios instalados actualmente.)
Preparando para reemplazar dpkg 1.15.5.6ubuntu4.5 (usando .../dpkg_1.15.5.6ubuntu4.6_amd64.deb) ...
Desempaquetando el reemplazo de dpkg ...
dpkg: error al procesar /var/cache/apt/archives/dpkg_1.15.5.6ubuntu4.6_amd64.deb (--install):
 unable to create `/usr/lib/dpkg/mksplit.dpkg-new' (while processing `./usr/lib/dpkg/mksplit'): Invalid argument
dpkg-deb: el subproceso paste fue terminado por la señal (Broken pipe)
Se encontraron errores al procesar:
 /var/cache/apt/archives/dpkg_1.15.5.6ubuntu4.6_amd64.deb

-- >8 --

-- 8< -- Output of apt-cache policy dpkg

dpkg:
  Instalados: 1.15.5.6ubuntu4.5
  Candidato: 1.15.5.6ubuntu4.6
  Tabla de versión:
     1.15.5.6ubuntu4.6 0
        500 http://es.archive.ubuntu.com/ubuntu/ lucid-updates/main Packages
 *** 1.15.5.6ubuntu4.5 0
        500 http://security.ubuntu.com/ubuntu/ lucid-security/main Packages
        100 /var/lib/dpkg/status
     1.15.5.6ubuntu4 0
        500 http://es.archive.ubuntu.com/ubuntu/ lucid/main Packages

-- >8 --