no way to update ubuntu from the distribution 12.04 to the 14.04 LTSs

the message was: "An unresolvable problem occurred while calculating the upgrade."
if I do: "grep Broken /var/log/dist-upgrade/apt.log" I got a lot of Broken packages with unresolved dependencies or conflicts, e.g.:
Broken libglib2.0-0:amd64 Rompe on libgnome-desktop-3-2 [ amd64 ] < 3.4.2-0ubuntu0.2 > ( libs ) (< 3.4.2-2)
Broken python3:amd64 Dipende on python3.4 [ amd64 ] < none -> 3.4.0-2ubuntu1 > ( python ) (>= 3.4.0-0~)
Broken tex-common:amd64 Rompe on texlive-common [ amd64 ] < 2009-15 > ( tex ) (< 2010)
Broken cups-filters:amd64 Va in conflitto on foomatic-filters [ amd64 ] < 4.0.16-0ubuntu0.2 -> 4.0.17-1ubuntu1 > ( universe/text )
Broken cups-filters:amd64 Va in conflitto on ghostscript-cups [ amd64 ] < 9.05~dfsg-0ubuntu4.2 > ( text )
Broken python3-gi:amd64 Dipende on python3 [ amd64 ] < 3.2.3-0ubuntu1.2 -> 3.4.0-0ubuntu2 > ( python ) (< 3.5)
Broken python3-minimal:amd64 Dipende on python3.4-minimal [ amd64 ] < none -> 3.4.0-2ubuntu1 > ( python ) (>= 3.4.0-0~)
Broken dh-python:amd64 Dipende on python3:any [ amd64 ] < none > ( none ) (>= 3.3.2-2~)
Broken lsb-release:amd64 Dipende on python3 [ amd64 ] < 3.2.3-0ubuntu1.2 -> 3.4.0-0ubuntu2 > ( python )
Broken texlive-base:amd64 Va in conflitto on texlive-doc-base [ amd64 ] < 2009-2 > ( tex )
Broken libunity9:amd64 Rompe on unity-common [ amd64 ] < 5.20.0-0ubuntu3 > ( gnome ) (< 7.1.2)
Broken xz-utils:amd64 Va in conflitto on xz-lzma [ amd64 ] < 5.1.1alpha+20110809-3 > ( utils )
Broken python3-apt:amd64 Dipende on python3 [ amd64 ] < 3.2.3-0ubuntu1.2 -> 3.4.0-0ubuntu2 > ( python ) (< 3.5)
Broken python3-dbus:amd64 Dipende on python3 [ amd64 ] < 3.2.3-0ubuntu1.2 -> 3.4.0-0ubuntu2 > ( python ) (>= 3.4~)
Broken gnome-menus:amd64 Dipende on python3:any [ amd64 ] < none > ( none ) (>= 3.1~)
Broken libgoa-1.0-0b:amd64 Va in conflitto on libgoa-1.0-0 [ amd64 ] < 3.4.0-0ubuntu1.1 > ( libs )
Broken rhythmbox:amd64 Dipende on python3 [ amd64 ] < 3.2.3-0ubuntu1.2 -> 3.4.0-0ubuntu2 > ( python ) (< 3.5)
Broken software-properties-gtk:amd64 Dipende on python3 [ amd64 ] < 3.2.3-0ubuntu1.2 -> 3.4.0-0ubuntu2 > ( python )
Broken aptdaemon:amd64 Dipende on python3:any [ amd64 ] < none > ( none ) (>= 3.2~)
Broken libnetcdfc7:amd64 Rompe on libnetcdf6 [ amd64 ] < 1:4.1.1-6 > ( libs ) (< 1:4.1.1-7~

..and many many others..

I really don't know what to do.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager 1:0.156.14.17
ProcVersionSignature: Ubuntu 3.2.0-67.101-generic 3.2.60
Uname: Linux 3.2.0-67-generic x86_64
ApportVersion: 2.0.1-0ubuntu17.6
Architecture: amd64
Date: Wed Aug 13 00:33:27 2014
GsettingsChanges:

InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120823.1)
MarkForUpload: True
PackageArchitecture: all
SourcePackage: update-manager
Symptom: ubuntu-release-upgrader-core
UpgradeStatus: Upgraded to precise on 2014-08-12 (0 days ago)