Help with Bizarre Error

I'm getting a very bizarre error:

NameError in LandlordsController#search

uninitialized constant Landlord

RAILS_ROOT: /var/rails/rental/public/../config/..
Application Trace | Framework Trace | Full Trace

/usr/lib/ruby/gems/1.8/gems/activesupport-1.3.1/lib/active_support/dependencies.rb:100:in
`const_missing'
/usr/lib/ruby/gems/1.8/gems/activesupport-1.3.1/lib/active_support/dependencies.rb:131:in
`const_missing'
/usr/lib/ruby/gems/1.8/gems/activesupport-1.3.1/lib/active_support/dependencies.rb:133:in
`send'
/usr/lib/ruby/gems/1.8/gems/activesupport-1.3.1/lib/active_support/dependencies.rb:133:in
`const_missing'
#{RAILS_ROOT}/app/controllers/landlords_controller.rb:38:in `search'

Here is the call in the landlords_controller.rb file:

  def search
    @landlords = Landlord.find(:all, :order=>'company_name',
:conditions => ["company_id = ? AND active = 1",
@session['user'].company_id])
  end

Landlord is a model class, that is defined in landlord.rb in the models
directory.

The really bizarre part is this: I made a duplicate of the application
directory and the copies are identical. When running in one of the app
directorys, the application runs fine. In the other directory, it give
the error. This same behavior occurs when using both lighttpd and
webrick

Ruby: 1.8.2
Rails: 1.1.6
MySQL: 4.1

Any ideas/help would be greatly appreciated.

Thanks,