Observer + acts_as_taggable plugin = dead app

so i have found that if i try to place an observer on a model that is
using the acts_as_taggable plugin, my app will not start up. this is
what i get in the mongrel startup log

`method_missing': undefined local variable or method `acts_as_taggable'
for Profile:Class (NameError)

if i comment out either the observer in the config/environment.rb or
the acts_as_taggable it starts up fine.

any help would me majorly appreciated