Installer is a prime example of a potentially community maintained external package. It lives at http://www.squeaksource.com/installer.html
Trunk started out with an old version of Installer for no good reason and has diverged since then. 
Matthew pulled some Installer stuff he needed into Trunk awhile back. Some fixes from a Pharo guy went into the squeaksource version and Trunk wouldn't likely have those. 
A merge of Trunk Installer with the one on squeaksource is needed to bring Trunk to the latest.  
A complaint was made that Installer doesn't have tests but it does on squeaksource. The tests were made to run on the enhanced version of SUnit at http://www.squeaksource.com/testing.html
which was intended for automated testing and logging. 
A bit of work is needed to bring Trunk up to the latest state and to get the tests working. 

Ken,
from my iPhone

On 2011-05-08, at 5:49, Chris Cunnington <smalltalktelevision at gmail.com> wrote:

> Hi Ken,
> 
> This is an interesting question. I tried some of the documentation examples and they worked. And then the error you mention appeared.
> 
> It sounds to me like you need to talk to the maintainer of Installer. Perhaps it doesn't have one at this time. Or perhaps you're the most likely person on this board he'd actually talk to.
> 
> Chris
>