How to pass PHP variable to javascript in Drupal 7

Javascript works fine, but i need to get my_var variable from module. At the moment its not working.

Clear my page cache and browser cache several times.

The variable 'my_var' is showing value on front end but not on backend/admin side.

Front end theme is: Bartik
Backend/Admin theme: Seven I don't know if this help.

All other variables are available on Admin side from Drupal.settings, except the one I pass from my custom module.

This works well on both themes

alert(Drupal.settings.basePath);

Here is my code:

MY_MODULE.module

/**
 * Implements hook_page_build().
 */
function MY_MODULE_page_build(&$page) {
    ctools_include('modal');
    ctools_modal_add_js();

    // HERE it is calling the js
    drupal_add_js(array('MY_MODULE' => array('my_var' => 'MY_VALUE'),), 'setting');
    drupal_add_js(drupal_get_path('module', 'MY_MODULE') . '/js/MY_MODULE.js');
}

MY_MODULE.js

(function ($) {
    Drupal.behaviors.MY_MODULE = {
    attach: function(context) {
        alert("test");
        alert(Drupal.settings.MY_MODULE.my_var);
    }
  }
})(jQuery);

On front end it alerts test followed by MY_VALUE
BUT On admin side it show test in alert then Firebug shows me:

Uncaught TypeError: Cannot read property 'my_var' of undefined 

Any help would be appreciated.