I have upgrade my ubuntu from 11.10 to 12.04. at last i can found that when i tries to install some packages it shows a error. after reading some blog i tried to fix that error by "sudo dpkg --configure -a". but when i run this command it show another error this Setting up colord (0.1.16-2) ... useradd: cannot lock /etc/passwd; try again later. adduser: `/usr/sbin/useradd -d /var/lib/colord -g colord -s /bin/false -u 115 colord' returned error code 1. Exiting. dpkg: error processing colord (--configure): subprocess installed post-installation script returned error exit status 1 Setting up whoopsie (0.1.32) ... useradd: cannot lock /etc/passwd; try again later. adduser: `/usr/sbin/useradd -d /nonexistent -g whoopsie -s /bin/false -u 115 whoopsie' returned error code 1. Exiting. dpkg: error processing whoopsie (--configure): subprocess installed post-installation script returned error exit status 1 Setting up lightdm (1.2.1-0ubuntu1) ... Adding system user `lightdm' (UID 115) ... Adding new user `lightdm' (UID 115) with group `lightdm' ... useradd: cannot lock /etc/passwd; try again later. adduser: `/usr/sbin/useradd -d /var/lib/lightdm -g lightdm -s /bin/false -u 115 lightdm' returned error code 1. Exiting. dpkg: error processing lightdm (--configure): subprocess installed post-installation script returned error exit status 1 dpkg: dependency problems prevent configuration of ubuntu-desktop: ubuntu-desktop depends on lightdm; however: Package lightdm is not configured yet. dpkg: error processing ubuntu-desktop (--configure): dependency problems - leaving unconfigured Errors were encountered while processing: colord whoopsie lightdm ubuntu-desktop what can i do now ?