Seach tweets with geocode Twitter gem

ruby 1.9.3p286 (2012-10-12 revision 37165) [x86_64-darwin10.8.0]
gem twitter (4.4.1, 3.7.0)

the gem is this.
https://github.com/sferik/twitter

What I am trying to do is simply to search tweets from geocode.

@client = Twitter::Client.new(
:consumer_key => CONSUMER_KEY,
:consumer_secret => CONSUMER_SECRET,
:oauth_token => OAUTH_TOKEN,
:oauth_token_secret => OAUTH_TOKEN_SECRET
)

longitude = 140.3863
latitude = 35.76472
str = latitude.to_s + ‘,’ + longitude.to_s + ‘, 10km’

p @client.search(:geocode => str ).results

gives an error

/Users/soichi/.rvm/gems/ruby-1.9.3-p286/gems/twitter-4.4.1/lib/twitter/response/raise_error.rb:21:in
on_complete': Could not authenticate you (Twitter::Error::Unauthorized) from /Users/soichi/.rvm/gems/ruby-1.9.3-p286/gems/faraday-0.8.4/lib/faraday/response.rb:9:inblock in call’

But the authentication should be fine because I have tried user_timeline
and got the results as expected.

Do you see the problem in my code?

soichi