undefined method `error_format' on execution of command exec rackup

[VinayBhalerao]

Hi,

I have followed exact same steps as described in the Configuration (Generic) section. Link: https://github.com/njyx/sentiment-grape-demo

When I try to start the API using command "exec rackup" I am getting below error

$ exec rackup
/home/3scale/heroku/sentiment-api-example/version_1/app/sentimentapi_v1.1.rb:8:in <class:SentimentApiV1_1>': undefined methoderror_format' for SentimentApiV1_1:Class (NoMethodError)
from /home/3scale/heroku/sentiment-api-example/version_1/app/sentimentapi_v1.1.rb:6:in <top (required)>' from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:55:inrequire'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:55:in require' from /home/3scale/heroku/sentiment-api-example/version_1/config.ru:4:inblock in

'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/builder.rb:55:in instance_eval' from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/builder.rb:55:ininitialize'
from /home/3scale/heroku/sentiment-api-example/version_1/config.ru:in new' from /home/3scale/heroku/sentiment-api-example/version_1/config.ru:in'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/builder.rb:49:in eval' from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/builder.rb:49:innew_from_string'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/builder.rb:40:in parse_file' from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/server.rb:277:inbuild_app_and_options_from_config'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/server.rb:199:in app' from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/server.rb:314:inwrapped_app'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/server.rb:250:in start' from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/lib/rack/server.rb:141:instart'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/rack-1.5.2/bin/rackup:4:in <top (required)>' from /usr/local/rvm/gems/ruby-1.9.3-p392/bin/rackup:23:inload'
from /usr/local/rvm/gems/ruby-1.9.3-p392/bin/rackup:23:in <main>' from /usr/local/rvm/gems/ruby-1.9.3-p392/bin/ruby_noexec_wrapper:14:ineval'
from /usr/local/rvm/gems/ruby-1.9.3-p392/bin/ruby_noexec_wrapper:14:in `'

Connection to 10.10.110.253 closed.

Ruby version:
root# ruby -v

ruby 1.8.7 (2012-02-08 patchlevel 358) [universal-darwin12.0]

Am I doing something wrong?
Your help would be appreciated.

Best Regards,
Vinay Bhalerao