无法在Ubuntu上安装openssh-server

我从http://www.ubuntu.com/download/desktop下载了Ubuntu 14.04.3 LTS（64位），现在无法安装openssh-server。当我尝试时会发生以下情况：

ubuntu@ubuntu:~$ sudo apt-get install openssh-server
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that ytou 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:
 openssh-server : Depends: openssh-client(= 1:6.6p1-2ubuntu1) but 1:6.6p1-2ubuntu2 is to be installed
        Recommends: ncurses-term but it is not going to be installed
        Recommends: ssh-import-id but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

有任何想法吗？