We're sorry, but something went wrong

I'm learning about Paperclip: Attaching Files in Rails, following this link http://rdoc.info/gems/paperclip/2.3.11/file/README.md

I place these code to display image on show.html.erb

<%= image_tag @user.photo.url %>
<%= image_tag @user.photo.url(:thumb) %>

On new page, I browse a file (.png) from my computer and click create. Then I got the error

We're sorry, but something went wrong.

When I check on development.log. I found these errors

Status: 500 Internal Server Error
  The system cannot find the path specified
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/utils.rb:486:in
`initialize'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/utils.rb:486:in
`new'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/utils.rb:486:in
`parse_multipart'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/utils.rb:471:in
`loop'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/utils.rb:471:in
`parse_multipart'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/request.rb:268:in
`parse_multipart'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/request.rb:146:in
`POST'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/methodoverride.rb:15:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/actionpack-2.3.8/lib/action_controller/params_parser.rb:15:in
`call'
    C:/jruby/jruby-1.5.0/lib/r开发者_JAVA技巧uby/gems/1.8/gems/actionpack-2.3.8/lib/action_controller/session/cookie_store.rb:99:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/actionpack-2.3.8/lib/action_controller/failsafe.rb:26:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/lock.rb:11:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/actionpack-2.3.8/lib/action_controller/dispatcher.rb:114:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/actionpack-2.3.8/lib/action_controller/reloader.rb:34:in
`run'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/actionpack-2.3.8/lib/action_controller/dispatcher.rb:108:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/rails/rack/static.rb:31:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/urlmap.rb:49:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/urlmap.rb:41:in
`each'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/urlmap.rb:41:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/rails/rack/log_tailer.rb:17:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/content_length.rb:13:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/chunked.rb:15:in
`call'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/handler/mongrel.rb:67:in
`process'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/mongrel-1.1.5-java/lib/mongrel.rb:159:in
`process_client'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/mongrel-1.1.5-java/lib/mongrel.rb:158:in
`each'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/mongrel-1.1.5-java/lib/mongrel.rb:158:in
`process_client'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/mongrel-1.1.5-java/lib/mongrel.rb:285:in
`run'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/mongrel-1.1.5-java/lib/mongrel.rb:285:in
`initialize'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/mongrel-1.1.5-java/lib/mongrel.rb:285:in
`new'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/mongrel-1.1.5-java/lib/mongrel.rb:285:in
`run'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/mongrel-1.1.5-java/lib/mongrel.rb:268:in
`initialize'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/mongrel-1.1.5-java/lib/mongrel.rb:268:in
`new'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/mongrel-1.1.5-java/lib/mongrel.rb:268:in
`run'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rack-1.1.0/lib/rack/handler/mongrel.rb:38:in
`run'
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/commands/server.rb:111
    C:/jruby/jruby-1.5.0/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/commands/server.rb:31:in
`require'
    C:/jruby/jruby-1.5.0/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in
`require'
    ./script/server:3
    ./script/server:2:in `load'
    -e:2

How to solve this problem? Please help!

this could be because of non-existing temp directory ( on linux it is /tmp) or the user running the app does not have read/write permissions for that.