Why do I get this error when tried to copy Rails App to the other server?

Why do I get this error when tried to copy Rails App to the other server?

I'm trying to bring Rails App that's already working to the other new server.
I've brought entire folder of Rails app, set up everything up, and it's
ready for working.
In new server, it shows exactly the same gems as the gems in old server
when I command bundle list All the versions of gems are the same, too.
Then I've imported ****_production database to new server.
However, it returns this error below when it loads the page. Why? how can
I fix this?
Passenger encountered the following error: The application spawner server
exited unexpectedly: Unexpected end-of-file detected.
Exception class: PhusionPassenger::Rack::ApplicationSpawner::Error
Backtrace:
# File Line Location
0
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/rack/application_spawner.rb
134 in `rescue in start'
1
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/rack/application_spawner.rb
129 in `start'
2
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/spawn_manager.rb
253 in `block (2 levels) in spawn_rack_application'
3
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/abstract_server_collection.rb
132 in `lookup_or_add'
4
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/spawn_manager.rb
246 in `block in spawn_rack_application'
5
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/abstract_server_collection.rb
82 in `block in synchronize'
6 prelude> 10:in `synchronize'
7
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/abstract_server_collection.rb
79 in `synchronize'
8
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/spawn_manager.rb
244 in `spawn_rack_application'
9
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/spawn_manager.rb
137 in `spawn_application'
10
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/spawn_manager.rb
275 in `handle_spawn_application'
11
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/abstract_server.rb
357 in `server_main_loop'
12
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/lib/phusion_passenger/abstract_server.rb
206 in `start_synchronously'
13
/usr/local/lib/ruby/gems/1.9.1/gems/passenger-3.0.9/helper-scripts/passenger-spawn-server
99 in `'