Push Notifications weird problem

Hello, i am developing an android app which contains push notifications. The app works properly with the push notif. service but there is a small problem. When app opens, it logins to acs, retrieves device token and then it subscribes to a channel. But if i close the app and then reopen it, the function CloudPush.retrieveDeviceToken() cant run. Here is the code

alloy.js

var com = require('common');
com.loginToACS();

common.js

var Cloud = require('ti.cloud');
exports.loginToACS = function() {
    if (Titanium.Network.networkType == Titanium.Network.NETWORK_NONE) {
        alert(L('alert_nonetwork'));        
    } else {
        Cloud.debug = true;
        // Login to Titanium Cloud
        Cloud.Users.login({
            login : 'myLogin',
            password : 'myPass'
        }, function(e) {
            if (e.success) {
                Ti.API.info('Login success!');
                registerForACSNotifications();
            } else {
                alert('Error: ' + ((e.error && e.message) || JSON.stringify(e)));
            }
        });
    }
};
 
// Retrieve device token and subscribe to channel in success
var CloudPush = require('ti.cloudpush');
var deviceToken = null;
function registerForACSNotifications() {
    try {
        CloudPush.retrieveDeviceToken({
            success : function deviceTokenSuccess(e) {
                Cloud.PushNotifications.subscribe({
                    channel : 'myChannel',
                    type : 'gcm',
                    device_token : e.deviceToken
                }, function(e) {
                    if (e.success) {
                        Ti.API.info('Success! ' + ((e.error && e.message) || JSON.stringify(e)));
                    } else {
                        Ti.API.info('Error:\\n ' + ((e.error && e.message) || JSON.stringify(e)));
                    }
                });
            },
            error : function deviceTokenError(e) {
                Ti.API.info('Failed to register for push! ' + e.error);
            }
        });
        CloudPush.enabled = true;
        CloudPush.addEventListener('callback', function(evt) {
            Ti.API.info("evt.payload: " + evt.payload);
        });
    } catch(x) {
        alert(L('alert_acsregerror'));
    }
}

When the app reopens, it goes to catch(x) { alert(L('alert_acsregerror')); } Where is the problem? Should i get deviceToken once and then save it locally and use it for ever? The app must get device token every time it opens?