【Unity5】ビルド時にだけCS1061エラーが発生する

###前提・実現したいこと
こちらのUnityプロジェクトをビルドしたい。

###発生している問題・エラーメッセージ

Assets\ThetaStreaming\ThetaWifiStreaming.cs(37,11): error CS1061: 'WebRequest' does not contain a definition for 'Timeout' and no extension method 'Timeout' accepting a first argument of type 'WebRequest' could be found (are you missing a using directive or an assembly reference?)
Assets\ThetaStreaming\ThetaWifiStreaming.cs(40,31): error CS0117: 'Encoding' does not contain a definition for 'Default'
Assets\ThetaStreaming\ThetaWifiStreaming.cs(46,11): error CS1061: 'WebRequest' does not contain a definition for 'ContentLength' and no extension method 'ContentLength' accepting a first argument of type 'WebRequest' could be found (are you missing a using directive or an assembly reference?)
Assets\ThetaStreaming\ThetaWifiStreaming.cs(51,30): error CS1061: 'WebRequest' does not contain a definition for 'GetRequestStream' and no extension method 'GetRequestStream' accepting a first argument of type 'WebRequest' could be found (are you missing a using directive or an assembly reference?)
Assets\ThetaStreaming\ThetaWifiStreaming.cs(53,13): error CS1061: 'Stream' does not contain a definition for 'Close' and no extension method 'Close' accepting a first argument of type 'Stream' could be found (are you missing a using directive or an assembly reference?)
Assets\ThetaStreaming\ThetaWifiStreaming.cs(54,27): error CS1061: 'WebRequest' does not contain a definition for 'GetResponse' and no extension method 'GetResponse' accepting a first argument of type 'WebRequest' could be found (are you missing a using directive or an assembly reference?)
Assets\ThetaStreaming\ThetaWifiStreaming.cs(57,47): error CS0246: The type or namespace name 'BufferedStream' could not be found (are you missing a using directive or an assembly reference?)
Assets\ThetaStreaming\ThetaWifiStreaming.cs(102,31): error CS0117: 'Encoding' does not contain a definition for 'Default'
Error building Player because scripts had compiler errors

###該当のソースコード

csharp
1using UnityEngine;
2using System.Collections;
3using System.Net;
4using System.IO;
5using System.Text;
6using System.Collections;
7using System.Collections.Generic;
8using LitJson;
9
10public class ThetaWifiStreaming : MonoBehaviour {
11
12	private bool isLooping = true;
13	private Renderer myRenderer;
14	public string thetaUrl = "http://192.168.1.1:80";
15	private string executeCmd = "/osc/commands/execute";
16	public JsonData outputJson = new JsonData();
17
18	// Use this for initialization
19	IEnumerator Start () {
20		string jsonStr;
21		myRenderer = GetComponent<Renderer>();
22
23		jsonStr = "{" +
24			"\"name\" : \"camera.startSession\", " +
25			"\"parameters\": {} " +
26			"}";
27		yield return StartCoroutine( SendThetaCmd( jsonStr ) );
28		print( outputJson["results"]["sessionId"] );
29		string sessionId = (string)(outputJson["results"]["sessionId"]);
30
31		string url = thetaUrl + executeCmd;
32		var request = HttpWebRequest.Create (url);
33		HttpWebResponse response = null;
34		request.Method = "POST";
35		request.Timeout = (int)(30 * 10000f);
36		request.ContentType = "application/json;charset=utf-8";
37
38		byte[] postBytes = Encoding.Default.GetBytes ("{" +
39			"\"name\": \"camera._getLivePreview\"," +
40			"\"parameters\": { " +
41				"\"sessionId\": \"" + sessionId +"\"" +
42				"}" +
43			"}");
44		request.ContentLength = postBytes.Length;
45
46		Stream reqStream = request.GetRequestStream ();
47		reqStream.Write (postBytes, 0, postBytes.Length);
48		reqStream.Close ();
49		Stream stream = request.GetResponse ().GetResponseStream ();
50
51		BinaryReader reader = new BinaryReader (new BufferedStream (stream), new System.Text.ASCIIEncoding ());
52
53		List<byte> imageBytes = new List<byte> ();
54		bool isLoadStart = false;
55		while( isLooping ) { 
56			byte byteData1 = reader.ReadByte ();
57			byte byteData2 = reader.ReadByte ();
58
59			if (!isLoadStart) {
60				if (byteData1 == 0xFF && byteData2 == 0xD8){
61					// mjpeg start! ( [0xFF 0xD8 ... )
62					imageBytes.Add(byteData1);
63					imageBytes.Add(byteData2);
64
65					isLoadStart = true;
66				}
67			} else {
68				imageBytes.Add(byteData1);
69				imageBytes.Add(byteData2);
70
71				if (byteData1 == 0xFF && byteData2 == 0xD9){
72					// mjpeg end (... 0xFF 0xD9] )
73
74					Texture2D tex = new Texture2D(2, 2);
75					tex.LoadImage ((byte[])imageBytes.ToArray ());
76					myRenderer.material.mainTexture = tex;
77					imageBytes.Clear();
78					yield return null;
79					isLoadStart = false;
80				}
81			}
82		}
83	}
84
85	public IEnumerator SendThetaCmd ( string inputJsonText ) {
86
87		Dictionary<string, string> header = new Dictionary<string, string> ();
88		header.Add ("Content-Type", "application/json; charset=UTF-8");
89
90		byte[] postBytes = Encoding.Default.GetBytes (inputJsonText);
91
92		string url = thetaUrl + executeCmd;
93		WWW myWww = new WWW (url, postBytes, header);
94		yield return myWww;
95
96		if (myWww.error == null) {
97			Debug.Log("Success");
98			outputJson = JsonMapper.ToObject( myWww.text );
99			print( myWww.text );
100		}
101		else{
102			Debug.Log("Failure");          
103		}
104	}	
105	// Update is called once per frame
106	void Update () {
107		if ( Input.GetKey(KeyCode.Escape) ) {
108			isLooping = false;
109		}
110	}
111}

###試したこと
0. ThetaWifiStreamingDemoシーンの動作確認->上記のソースコード含め全て正常に動作することを確認
0. BuildSettingでPlatformをWindowsStoreに切り替え、Unity C# Projectsにチェック（後にHololensへのビルドを考えているためこのようにしています）
0. Buildボタンを押し、Appフォルダを新規作成しその中にビルド->その後問題のエラーが発生

###補足情報(言語/FW/ツール等のバージョンなど)
Unity 5.6.4f

エディタ上では動作し、スクリプトでも名前空間の参照もできてるようなのですが、なぜかCS1061エラーがでてしまいます。
分かる方いらっしゃいましたら、よろしくお願いいたします。