Pode ser causado pela falta de pacotes no seu repositório. Tente mudar para o servidor principal.
Veja: link
Em seguida, execute novamente o gerenciador de atualização e instale as atualizações.
Estou usando o Ubuntu 11.10. Eu tentei com todas as opções como sudo apt-get update e sudo apt-get upgrade Estou ficando problema para muitos softwares enquanto instalando no centro de software, mostra erro 'não encontrado lá não é software chamado' ------ 'em suas fontes.
Também este é um problema ao instalar o gnome-shell.
sanket@sanket-Dell-System-XPS-L502X:~$ sudo apt-get install gnome-shell
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
gnome-shell : Depends: gjs (>= 1.29.18) but it is not installable
Depends: libgjs0c (>= 1.29.18) but it is not installable
Depends: caribou but it is not installable
Depends: cups-pk-helper but it is not installable
Depends: mesa-utils but it is not installable
Recommends: gnome-themes-standard but it is not going to be installed
Recommends: gnome-session-fallback but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
Existe algum problema com o Repositório, o que deve ser feito ????