I'm getting some strange errors lately whenever trying to apt-get install anything. Here's an example from trying to install fluidsynth.

$ sudo apt-get install libfluidsynth1

Reading package lists... Done

Building dependency tree       

Reading state information... Done

libfluidsynth1 is already the newest version.

libfluidsynth1 set to manually installed.

0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.

2 not fully installed or removed.

After this operation, 0 B of additional disk space will be used.

Do you want to continue [Y/n]? y

Setting up postgresql-9.1 (9.1.10-0ubuntu12.04) ...

 * Starting PostgreSQL 9.1 database server                                                                                                                     * The PostgreSQL server failed to start. Please check the log output:

2013-11-03 14:21:42 EST FATAL:  could not access private key file "server.key": No such file or directory

                                                                                                                                                       [fail]

invoke-rc.d: initscript postgresql, action "start" failed.

dpkg: error processing postgresql-9.1 (--configure):

 subprocess installed post-installation script returned error exit status 1

dpkg: dependency problems prevent configuration of postgresql:

 postgresql depends on postgresql-9.1; however:

  Package postgresql-9.1 is not configured yet.

dpkg: error processing postgresql (--configure):

 dependency problems - leaving unconfigured

No apport report written because the error message indicates its a followup error from a previous failure.

                                                                                                          Errors were encountered while processing:

 postgresql-9.1

 postgresql

E: Sub-process /usr/bin/dpkg returned an error code (1)

I'm running 12.04. What's causing this and how do I address it? It happens for installing lots of things, and seems to suggest I need to initialize postgresql or something. I don't recall having fiddled with postgres, so I'm not sure why this suddenly became problematic.