Angular JS - Issue while separating Services.js

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AngularJs

I have a base.js
and a services.js in My angular App
but when I move the code to Services.js. The Application Breaks

App.js - This Works

var App = angular.module("App", ["ui.router", "ui.bootstrap", "ngAnimate","toastr"])

.service("utilServices", function ($rootScope, toastr) {
var mem = {};
return {
    storeVal: function (key, value) {
        mem[key] = value;
    },
    fetchVal: function (key) {
        return mem[key];
    },
    showAlert: function (msg, msgType, appVal) {
        if (msgType === "success") {
            return toastr.success(msg, appVal);
       }
        return false;
    }
};
});
App.service("alertService", function (utilServices) {
var appVal = utilServices.fetchVal("vTitle") + " says";
this.Display = function (msg,msgtype) { return utilServices.showAlert(msg,msgtype,appVal); };

return false;
});
App.controller("baseController", window.baseController);

But the same when I move the services to a different file "Services.js"
..........App.js -

var App = angular.module("App", ["ui.router", "ui.bootstrap", "ngAnimate", "toastr"]);

App.service("utilServices", window.commonServices);

App.controller("baseController", window.baseController);

.........Services.js

 var mem = {};
 window.commonServices = function($rootScope, toastr) {
   return {
    storeVal: function(key, value) {
        mem[key] = value;

    },
    fetchVal: function(key) {

        return mem[key];
    },
    showAlert: function(msg, msgType, appVal) {
        if (msgType === "success") {
            return toastr.success(msg, appVal);
        }
        return false;
    }
};


};
window.commonServices.$inject = ["$rootScope", "toastr"];

I get this error in the developer console of My Browser (Chrome) -

TypeError: Cannot read property 'prototype' of undefined
at Object.instantiate (angular.js:4485)
at Object.<anonymous> (angular.js:4346)
at Object.invoke (angular.js:4478)
at Object.enforcedReturnValue [as $get] (angular.js:4330)
at Object.invoke (angular.js:4478)
at angular.js:4295
at getService (angular.js:4437)
at Object.invoke (angular.js:4469)
at extend.instance (angular.js:9136)
at nodeLinkFn (angular.js:8248)

This only occurs when I move the code of service to a separate a file and not when it is declared within the app.js file. I think it has something to do with the $.inject. I'm still a newbie learning the ropes. Any Help would be greatly appreciated :)