Ferret problem, load missing constant

I am having problems with ferret server. My site is crashing sometimes (
I can’t identify when or why! ). The error it throws is the following:

A LoadError occurred in application#row:

Expected
/sites/xxx/releases/20090608140506/app/controllers/thursday_newsletters_controller.rb
to define ThursdayNewslettersController
/usr/lib/ruby/gems/1.8/gems/activesupport-2.0.2/lib/active_support/dependencies.rb:249:in
`load_missing_constant’

This error also happens to other controllers that have a ferret server
associated in the model.

Can this be a problem of performance? If so, is there a way to have more
than one server running ferret?
Maybe is a problem with activesupport 2.0.2?

Thanks!