I'm unsure as to why I'm getting the following error when apache is rebooted:

Invalid command 'VirtualDocumentRoot', perhaps misspelled or defined by a module not included in the server configuration Action 'start' failed.

The snippet it is referring to is this:

<VirtualHost *:80>
        ServerAdmin [email protected]
        VirtualDocumentRoot /local/www/staging/%1

        ServerAlias *.staging.mydomain.com
</VirtualHost>

I assumed it was a misspelling as it said, but it was copied directly from another server of mine. It works perfect there. Any ideas?