Non-existent in that revision error when trying to install

When I try to install Engines, I get this error:

[acompw@a-c12 railsapp]$ ruby script/plugin install engines svn: URL
‘svn://rubyforge.org/var/svn/laszlo-plugin/rails/plugins’ non-existent
in that revision

Can anyone shed some light on what this error means and what steps I can
take to resolve it.

Thanks,
Ben

Anyone?