Debian 6 Sqeeze で未解決の依存関係の問題

VirtualBox 4.2.14 VMとDebian 6 Sqeezeをゲストシステムとして使用しており、Nginxを（再）インストールしようとしましたが、動作しません。

root@devmv:~# apt-get install nginx
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:
 nginx : Depends: nginx-full but it is not going to be installed or
                  nginx-light but it is not going to be installed
E: Broken packages

または、Synapticパッケージマネージャでも同じです。

aptitude欠落している依存関係に関する追加情報を提供します。

root@devmv:~# aptitude install nginx
The following NEW packages will be installed:
  nginx nginx-common{a} nginx-full{ab} 
0 packages upgraded, 3 newly installed, 0 to remove and 0 not upgraded.
Need to get 580 kB/645 kB of archives. After unpacking 1,391 kB will be used.
The following packages have unmet dependencies:
  nginx-full: Depends: libgeoip1 (>= 1.4.8+dfsg) but 1.4.7~beta6+dfsg-1 is installed.
              Depends: libpcre3 (>= 8.10) but 8.02-1.1 is installed.
              Depends: libssl1.0.0 (>= 1.0.1) which is a virtual package.
The following actions will resolve these dependencies:

     Keep the following packages at their current version:
1)     nginx [Not Installed]                              
2)     nginx-full [Not Installed]                         



Accept this solution? [Y/n/q/?]

通常apt-get、パッケージをインストールする必要があるだけでなく、その依存関係も再帰的にインストールする必要があります。そうですか？ここで何の問題がありますか？

---

編集する：

/etc/apt/sources.list

# 

# deb cdrom:[Debian GNU/Linux 6.0.6 _Squeeze_ - Official amd64 NETINST Binary-1 20120930-15:53]/ squeeze main

#deb cdrom:[Debian GNU/Linux 6.0.6 _Squeeze_ - Official amd64 NETINST Binary-1 20120930-15:53]/ squeeze main

deb http://ftp.de.debian.org/debian/ squeeze main
deb-src http://ftp.de.debian.org/debian/ squeeze main

deb http://security.debian.org/ squeeze/updates main
deb-src http://security.debian.org/ squeeze/updates main

# squeeze-updates, previously known as 'volatile'
deb http://ftp.de.debian.org/debian/ squeeze-updates main
deb-src http://ftp.de.debian.org/debian/ squeeze-updates main

# For Nginx & PHP
deb http://packages.dotdeb.org stable all
deb http://packages.dotdeb.org squeeze-php54 all
deb-src http://packages.dotdeb.org squeeze-php54 all

# psmisc 22.16
deb http://ftp.at.debian.org/debian-backports/ squeeze-backports main

/etc/apt/sources.list.d空いた。