gem installation with Ruby2 x64 - ruby-on-rails

Question

I'm trying to install rails, but before I need to install devkit correctly.
So I'm making the normal procedure but I don't understand what's wrong. I'm using ruby 2 x64, and I tried with the DevKit x32 and x64. this is with the devkit x64. What can be wrong in here..? Thank You.
c:\DevKit>gem install json
Temporarily enhancing PATH to include DevKit...
Building native extensions. This could take a while...
ERROR: Error installing json:
ERROR: Failed to build gem native extension.
C:/Ruby200-x64/bin/ruby.exe extconf.rb
creating Makefile
make
generating generator-x64-mingw32.def
compiling generator.c
linking shared-object json/ext/generator.so
make install
/usr/bin/install -c -m 0755 generator.so C:/Ruby200-x64/lib/ruby/gems/2.0.0/gems
/json-1.8.0/lib/C/Ruby200-x64/lib/ruby/site_ruby/2.0.0/x64-msvcrt/json/ext
/usr/bin/install: cannot create regular file `C:/Ruby200-x64/lib/ruby/gems/2.0.0
/gems/json-1.8.0/lib/C/Ruby200-x64/lib/ruby/site_ruby/2.0.0/x64-msvcrt/json/ext'
: No such file or directory
make: *** [install-so] Error 1
Gem files will remain installed in C:/Ruby200-x64/lib/ruby/gems/2.0.0/gems/json-
1.8.0 for inspection.
Results logged to C:/Ruby200-x64/lib/ruby/gems/2.0.0/gems/json-1.8.0/ext/json/ex
t/generator/gem_make.out
NOTE: Before I installed with "ruby dk.rb install -f" in both x32 and x64 cases.
EDIT: For who is attempting to reply about the ruby dk.rb etc. procedure, I've done multiple times this:
c:\DevKit>ruby dk.rb init
Initialization complete! Please review and modify the auto-generated
'config.yml' file to ensure it contains the root directories to all
of the installed Rubies you want enhanced by the DevKit.
c:\DevKit>ruby dk.rb review
Based upon the settings in the 'config.yml' file generated
from running 'ruby dk.rb init' and any of your customizations,
DevKit functionality will be injected into the following Rubies
when you run 'ruby dk.rb install'.
C:/Ruby200-x64
c:\DevKit>ruby dk.rb install -f
[WARN] Updating (with backup) existing gem override for 'C:/Ruby200-x64'
[WARN] Updating (with backup) DevKit helper library for 'C:/Ruby200-x64'

Answer 1

I have also windows with installed java,jdk
I tried
ruby 2.0.0p0 (2013-02-24) [i386-mingw32]
C:\Users\rajarshid>gem install json --platform=ruby
Temporarily enhancing PATH to include DevKit...
Building native extensions. This could take a while...
Successfully installed json-1.8.0
Parsing documentation for json-1.8.0
unable to convert "\x90" from ASCII-8BIT to UTF-8 for lib/json/ext/generator.so, skipping
unable to convert "\x90" from ASCII-8BIT to UTF-8 for lib/json/ext/parser.so, skipping
Installing ri documentation for json-1.8.0
Done installing documentation for json (2 sec).
1 gem installed
Please check whether dev kit install properly or not
ruby dk.rb review
https://github.com/oneclick/rubyinstaller/wiki/Development-Kit