Ti.Utils.base64encode undefined in iOS

I made a project that in the beginning was made for Android, then I added the support for iOS devices, but when I try to run the project in the iOS emulator I've got the following error:

> [ERROR] : message = "'undefined' is not an object (evaluating 'Ti.Utils.base64encode')";

and the code is

var auth = 'Basic ' + Ti.Utils.base64encode(this.cachedUsername  + ':' + this.cachedPassword);

The above code runs fine in Android. I tried to delete the build folder as suggested by another post I found, but without success.

I'm running OS X 10.9.3, Xcode 5.1.1, iOS SDK 7.1

Thanks for help