undefined method `acts_as_attachment' for :model

Hi all,

I installed aa_attachment (edge version) on a Debian Linux box a test
app and it worked fine there. Now when I install the same version on a
MacBookPro in my real app it gives me the undefined method. Somehow
the method_missing is not being set during plugin install?

While I understand the concept of method_missing in Ruby and how Rails
uses it, I am not sure how plugins in general and acts_as_attachment
in particular sets this up. I am digging thro the source but any
pointers would be very much welcome

Both machines have the same versions of Rails and Ruby. Any clues?

Thanks very much,