Ruby on Rails 500 Internal Server Error

I keep getting 500 internal server error after I moved my rails app to Server. Seems like everything is installed right (I have used other rails app to test if server is working), but when I move my main application I keep getting this 500 error. I'm kinda new in RoR and Stackoverflow.

my log/development.log:

Started GET "/" for 81.177.143.31 at 2015-07-25 15:41:51 +0300
Processing by CategoriesController#index as HTML
  Rendered layouts/_header_main.html.haml (0.7ms)
  Rendered categories/index.html.haml within layouts/application (3.0ms)
  Rendered contacts/_form.html.haml (2.0ms)
  Rendered layouts/_footer.html.haml (3.0ms)
Completed 500 Internal Server Error in 198ms

I'm using Thin as web-server.

Bundle:install and rake db:migrate worked just fine. Can't find any more additional logs so that's why I'm posting this error here.