Unity C# XmlDoc.LoadXml() il2cpp not implemented exception

Stuck with this for a couple of hours, turned out it's just a setting thing,

Answer from this post (http://forum.unity3d.com/threads/problem-when-loading-xml-at-runtime.141705/)

"In Player Settings, Other Settings, if you Api Compatibility Level is .NET 2.0 subset, you will get this error. With .NET 2.0, you will not. It does make your final app bigger, though."

Thought it's about asynchronous loading, changed to coroutine funtion, still got 'not implemented exception'

　　　　yield return, http://docs.unity3d.com/ScriptReference/WaitForSeconds.html
Change to mono 2.x doesn't help

not seem to be architecture related

Have not tried XmlSerializer

　　　　http://wiki.unity3d.com/index.php?title=Saving_and_Loading_Data:_XmlSerializer

Standard System.IO write worked

　　　　https://msdn.microsoft.com/en-us/library/8bh11f1k.aspx

Context:

I was trying to make the save/load funciton work on iphone

Application.dataPath

　　Unity Editor: <path to project folder>/Assets

　　iOS player: <path to player app bundle>/<AppName.app>/Data (this folder is read only)

　　Notice that the path is not consistent.　　

Application.persistentDataPath

　　This is where you should put your save file.

　　http://stackoverflow.com/questions/30218457/how-access-to-persistentdatapath-child-folders-on-ios-unity-deployment

　Resources folder

　　　　Don't try to write data here- it's supposed to be readonly. And the assets are compiled into packages, and only those that UnityEditor thinks are being used are included.

Application.streamingAssetPath

　　Contains the path to the StreamingAssets folder (Read Only).

　　http://docs.unity3d.com/ScriptReference/Application-streamingAssetsPath.html