Could not find RubyGem railties (>= 0) (Gem::LoadError) with the RailsInstaller - ruby-on-rails

Question

In Ruby on Rails, I am trying to install it on my Windows machine following the step-by-step instructions indicated in http://railsinstaller.org/windows
On step 7, it says we should type in this command:
$ rails g controller welcome index
And so I do:
PS C:\Sites\railsinstaller_demo> rails g controller welcome index
And I get this error:
C:/Program Files/ruby-1.9.2/lib/ruby/site_ruby/1.9.1/rubygems.rb:926:in
`report_activate_error': Could not find RubyGem railties (>= 0) (Gem::LoadError)
from C:/Program Files/ruby-1.9.2/lib/ruby/site_ruby/1.9.1/rubygems.rb:244:in
`activate_dep'
from C:/Program Files/ruby-1.9.2/lib/ruby/site_ruby/1.9.1/rubygems.rb:236:in `activate'
from C:/Program Files/ruby-1.9.2/lib/ruby/site_ruby/1.9.1/rubygems.rb:1307:in `gem'
from C:/RailsInstaller/Ruby1.9.3/bin/rails:18:in `<main>'
I have googled this error and read that the solution was to install de DevKit and so I did, but the problem remains.
What causes these errors?
Edit:
This is what appears when I run gem list:
PS C:\Sites\railsinstaller_demo> gem list
*** LOCAL GEMS ***
actionmailer (3.2.9)
actionpack (3.2.9)
activemodel (3.2.9)
activerecord (3.2.9)
activeresource (3.2.9)
activesupport (3.2.9)
arel (3.0.2)
builder (3.0.4)
erubis (2.7.0)
foreman (0.60.2)
hike (1.2.1)
i18n (0.6.1)
journey (1.0.4)
mail (2.4.4)
mime-types (1.19)
minitest (1.6.0)
multi_json (1.5.0)
polyglot (0.3.3)
rack (1.4.1)
rack-cache (1.2)
rack-ssl (1.3.2)
rack-test (0.6.2)
rake (0.8.7)
rdoc (2.5.8)
rest-client (1.6.7)
sequel (3.20.0)
sinatra (1.0)
sprockets (2.2.2)
taps (0.3.24)
thor (0.16.0)
tilt (1.3.3)
treetop (1.4.12)
tzinfo (0.3.35)
As suggested by #EricLeschinski I tried tu run "gem install rails" but this error appeared:
PS C:\Sites\railsinstaller_demo> gem install rails
ERROR: Error installing rails:
The 'json' native gem requires installed build tools.
Please update your PATH to include build tools or download the DevKit
from 'http://rubyinstaller.org/downloads' and follow the instructions
at 'http://github.com/oneclick/rubyinstaller/wiki/Development-Kit'
Final edit:
In the end, I don't how bad I messed up my initial installation, but I found this Youtube video http://www.youtube.com/watch?v=WUdDdiu8kBs which turned out to be the clearest way to install everything that I needed and had no problem at all following her instructions.

Answer 1

Could not find RubyGem railties
This error is due to the difference between the rails version you are using and the one defined in the Gemfile.
Try rails -v to check the rails version.
Reference : https://www.railstutorial.org/book/toy_app