Retrieving App Properties from Preferences and Settings

I am building a mobile app using Titanium SDK version 3.2.0.GA for iOS 6+ testing on an iPhone 4S. My host runs OSX 10.9.2 using Titanium Studio, build: 3.2.1.201402041146.

I am integrating Urban Airship into my App and want to use the Settings App to provide the Alias and Tags. In my Root.plist, I have two Text Fields defined, one for alias= 'user_name' and the other for Tags='segment'.

In my js code, I use Ti.App.Properties to get the values. I get value for the 'alias', it is passed to UrbanAirship properly and I can see it in my 'Device Tokens'. When I attempt to do the same thing for the tags, I get a script error "Invalid type passed to function". Here is the code I am using:

alias : Ti.App.Properties.getString('user_name'),
tags : Ti.App.Properties.getString('segment'),

????????