Package listed in MELPA, but not found in package install

I am currently trying to install ENSIME for emacs 24.3.1 following the instructions at https://github.com/ensime/ensime-emacs under the quick start; I've added

    (require 'package)
    (add-to-list 'package-archives
             '("melpa" . "http://melpa.milkbox.net/packages/") t)
    (package-initialize)

(when (not package-archive-contents)
  (package-refresh-contents))

to my .emacs file, as instructed. However, when I restart and do M-x package install [RETURN]ensime[RETURN], it returns [No Match] and indeed, I can't find it when I list the packages. However, I can easily find it at http://melpa.milkbox.net/#; what would be causing the discrepancy between what is available through the website and when can be installed from emacs?

Any help is much appreciated; Thank you!

I had to run M-x package-refresh-contents. Once I did that, the files were found.

Here's what my .emacs looks like:

(cond
 ((>= 24 emacs-major-version)
  (require 'package)
  (package-initialize)
  (add-to-list 'package-archives
           '("melpa-stable" . "http://stable.melpa.org/packages/") t)
  (package-refresh-contents)
 )
)

In my .emacs file I have

;; packages
(when (>= emacs-major-version 24)
  (require 'package)
  (package-initialize)
  (add-to-list 'package-archives '("melpa" . "http://melpa.milkbox.net/packages/") t)
  )

Then, M-x package-list-packages

C-s ensime

and there you go:

ensime 20140718.... available ENhanced Scala Interaction Mode for Emacs

Are you sure your emacs can actually get access to internet?

After doing the usual editing of .emacs to make melpa avalaible and restarting Emacs, I searched the list of packages for the one I wanted.

M-x package-list-packages
C-s <package_name>

Then I clicked on the name of the package and pressed the install button. I am unsure as to why M-x package-install RET <package_name> failed, but clicking the install button worked for me.