C:UsersGavin>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:/RailsInstaller/Ruby1.9.3/bin/ruby.exe extconf.rb
creating Makefile

make
Makefile:161: warning: overriding commands for target `install-so'
Makefile:160: warning: ignoring old commands for target `install-so'
Makefile:162: *** missing separator.  Stop.


Gem files will remain installed in C:/Ruby193/lib/ruby/gems/1.9.1/bin;/gems/json-1.7.5 for inspection.
Results logged to C:/Ruby193/lib/ruby/gems/1.9.1/bin;/gems/json-1.7.5/ext/json/ext/generator/gem_make.out