Passenger Apache 'undefined symbol: unixd_config'
===

I'm trying to get apache running with passenger. I did:  

    sudo gem install passenger
    sudo passenger-install-apache2-module

After installing the other things it told me to install (e.g. apache2-prefork-dev) I added the lines it said to add to the http.conf file, and it tells me there's a syntax error on the LoadModule line.

    user@machine:~$ sudo /usr/local/apache2/bin/apachectl restart
    httpd: Syntax error on line 174 of /usr/local/apache2/conf/httpd.conf: 
    Cannot load /var/lib/gems/1.8/gems/passenger-3.0.13/ext/apache2/mod_passenger.so into server: 
    /var/lib/gems/1.8/gems/passenger-3.0.13/ext/apache2/mod_passenger.so: undefined symbol: unixd_config

That is referring to the following code which it told me to add:

    174 LoadModule passenger_module /var/lib/gems/1.8/gems/passenger-3.0.13/ext/apache2/mod_passenger.so
    175 PassengerRoot /var/lib/gems/1.8/gems/passenger-3.0.13
    176 PassengerRuby /usr/bin/ruby1.8

Do you know why it can't find the unixd_config?

Thanks in advance!

Some info:
Rails v3.2.6, Ruby 1.9.2p320, gem v1.8.24, apache2 (I don't know how to find the version, but I know it's 2.x)

If it matters:

    178 <VirtualHost *:80>
    179     ServerName www.example.com
    180     DocumentRoot /home/dylan/private/project/public
    181 
    182     <Directory /home/dylan/private/project/public>
    183         Order allow,deny
    184         Allow from all
    185     </Directory>
    186 </VirtualHost>

(also I have no idea what to put for ServerName if you want to help me with that too...)