Setting Unity's stripping level to Strip Assemblies or Strip ByteCode from Player Settings -> Optimization causes (at least) some of the System.Net functionality fail.
To test the issue, I created a simple project that only tries to use System.Net.WebRequest.Create():
using UnityEngine;
using System.Net;
public class NetworkAccessTest : MonoBehaviour
{
void Start()
{
bool succeeded = false;
try
{
WebRequest.Create("http://www.google.com");
succeeded = true;
}
catch (System.Exception e)
{
Debug.Log(string.Format("Exception: {0}", e));
succeeded = false;
}
Debug.Log(string.Format("Web request creation succeeded: {0}", succeeded));
}
}
It works fine without stripping. But without sripping:
Exception: System.NotSupportedException: http://www.google.com/
at System.Net.WebRequest.GetCreator (System.String prefix) [0x00000] in :0
at System.Net.WebRequest.Create (System.Uri requestUri) [0x00000] in :0
at System.Net.WebRequest.Create (System.String requestUriString) [0x00000] in :0
at NetworkAccessTest.Start () [0x00000] in :0 
