to_specs': Could not find 'thor' (~> 0.17.0) - did find: [thor-0.18.1] (Gem::LoadError)

Question

I am getting error in padrino to_specs': Could not find 'thor' (~> 0.17.0) - did find: [thor-0.18.1] (Gem::LoadError) . I could not find what to do. I have installed even thor-0.15.0, thor-0.17.0 also , But it was not working. same error I was getting. Can any body suggest me, How best way to start padrino. It was working previously. But I don't know why now I am not able to start padrino.

Following Error I am getting
while I am doing : padrino start
/usr/share/ruby-rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/dependency.rb:298:in to_specs': Could not find 'thor' (~> 0.17.0) - did find: [thor-0.18.1,thor-0.15.4] (Gem::LoadError) <br/> from /usr/share/ruby-rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1268:inblock in activate_dependencies'
from /usr/share/ruby-rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1257:in each' <br/> from /usr/share/ruby-rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1257:inactivate_dependencies'
from /usr/share/ruby-rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1239:in activate' <br/> from /usr/share/ruby-rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_gem.rb:48:ingem'
from /usr/share/ruby-rvm/gems/ruby-1.9.3-p194/bin/padrino:22:in `'