Ultrasphinx::UsageError (Invalid class name "Place")

Hi, all ..

  My application can run normally on development environment ,but when i change it to production, I got the problem below:

Ultrasphinx::UsageError (Invalid class name "Place"): /vendor/plugins/ultrasphinx/lib/ultrasphinx/search/internals.rb:88:in `build _request_with_options' /vendor/plugins/ultrasphinx/lib/ultrasphinx/search/internals.rb:85:in `map' /vendor/plugins/ultrasphinx/lib/ultrasphinx/search/internals.rb:85:in `build _request_with_options' /vendor/plugins/ultrasphinx/lib/ultrasphinx/search.rb:333:in `run'

The Ultrasphinx configure , index and daemon:start all seem to have gone.

Does anyone have an idea on this ?

Thanks in advance.