uninitialized constant Rails (NameError) in Rails 3.213 -

when attempt visit rails site working or attempt run rake following error

uninitialized constant rails (nameerror)  /path/config/boot.rb:4:in `<top (required)>'  /path/config/environment.rb:11:in `require'  /path/config/environment.rb:11:in `<top (required)>' 

here line 4 of boot file

rails.root  = "#{file.dirname(__file__)}/.." unless defined?(rails.root) 

and line 11 of enviroment file
require file.join(file.dirname(__file__), 'boot')

the error seems that when call rails.root, perceives rails somehow uninitialized. ideas?

if more info needed let me know. thank in advance

try updating rubygems gem update --system. looks there issues , fixed in recent versions.

if not works after adding:

gem install bundler 

and after adding:

gem 'bundler' 

in line 2 in config/boot.rb (just after require 'rubygems')

please let me know