Getting a Build error for Windows Phone 8 Platform, It's working fine in PC

Error building Player: Exception: Error: method System.Void System.IO.File::AppendAllText(System.String,System.String) doesn't exist in target framework. It is referenced from Assembly-CSharp.dll at System.Void CSVReader::SaveScoreToCsv(Score).

Error: method System.String[] System.IO.File::ReadAllLines(System.String) doesn't exist in target framework. It is referenced from Assembly-CSharp.dll at System.Void CSVReader::ReadDescp(System.String).

Error: method System.String[] System.IO.File::ReadAllLines(System.String) doesn't exist in target framework. It is referenced from Assembly-CSharp.dll at System.Void CSVReader::ReadGeneralSetting().

Code for CSVReader is as following::

using UnityEngine; using System.Collections; using System.Collections.Generic; using System.IO; using System.Text; using System; using System.Linq; using UnityEngine.UI;

public class CSVReader : MonoBehaviour { public TextAsset QuestionMSTxt; public TextAsset scoreSettingText;

 public static GeneralSettings generalSettings;

 string[] lines = null;

 public static IList<MultipleQuestionAnswer> MCQList;
 public static ScoreSettings scoreSettings;
 public static GameDiscription GameDiscription;

 public Text TitleText;
 public Text DescriptionText;

 public GameObject HomeScreen;
 public GameObject UsernameInputContainer;

 void Awake()
 {
     ReadGeneralSetting();

     ReadGameDescription();

     if (GameDiscription != null)
     {
         TitleText.text = GameDiscription.heading;
         DescriptionText.text = GameDiscription.description;
     }

 }

 void Start()
 {
     if (QuestionMSTxt != null)
     {
         ReadquestionnaireCSV(FindCSV("MSQuestions.csv", QuestionMSTxt));
     }

     if (scoreSettingText != null)
     {
         ReadScoreSettingsCSV(FindCSV("ScoreSettings.csv", scoreSettingText));
     }

 }

 private string[] InitializeQuestions()
 {
     if (Application.platform == RuntimePlatform.WindowsPlayer)
     {
         int tmpIndex = Application.dataPath.LastIndexOf('/');
         if (tmpIndex > 0)
         {
             string tmpPath = Application.dataPath.Substring(0, tmpIndex);
             tmpPath += "/Configs/MSQuestions.csv";
             if (File.Exists(tmpPath))
             {
                 StreamReader sr = new StreamReader(File.OpenRead(tmpPath));
                 lines = sr.ReadToEnd().Split('\n');
                 sr.Close();
             }
         }
     }
     else
     {
         lines = QuestionMSTxt.text.Split('\n');
     }

     if (lines == null)
     {
         Debug.Log("Couldnt find Questionaire in EXE. Loading default");
         lines = QuestionMSTxt.text.Split('\n');
     }
     return lines;
 }

 string[] FindCSV(string path, TextAsset asset)
 {
     if (Application.platform == RuntimePlatform.WindowsPlayer)
     {
         Debug.Log(" FIND CSV : " + path);
         Debug.Log(generalSettings.configPath + path);
         
         if (File.Exists(generalSettings.configPath + path))
         {
             Debug.Log("in general settings");
             StreamReader sr = new StreamReader(File.OpenRead(generalSettings.configPath + path));
             lines = sr.ReadToEnd().Split('\n');
             sr.Close();
         }
         else
         {

             int tmpIndex = Application.dataPath.LastIndexOf('/');
             string tmpPath = Application.dataPath.Substring(0, tmpIndex);
             tmpPath += "/Configs/" + path;
             Debug.Log(tmpPath + "in else");
             if (File.Exists(tmpPath))
             {
                 Debug.Log("in ifd;lakj");
                 StreamReader sr = new StreamReader(File.OpenRead(tmpPath));
                 lines = sr.ReadToEnd().Split('\n');
                 sr.Close();
             }
         }
     }
     else
     {
         lines = asset.text.Split('\n');
     }

     if (lines == null)
     {
         Debug.Log("Couldnt find File in EXE. Loading default");
         lines = asset.text.Split('\n');
     }

     return lines;
 }

 void ReadScoreSettingsCSV(string[] data)
 {
     scoreSettings = new ScoreSettings();
     List<string[]> stringData = new List<string[]>();

     foreach (string s in data)
     {
         stringData.Add(s.Split(','));
     }

     int.TryParse(stringData[1][1], out scoreSettings.missionTimeScore);
     int.TryParse(stringData[2][1], out scoreSettings.missionTimerScore);
     int.TryParse(stringData[3][1], out scoreSettings.MapPuzzle);
     int.TryParse(stringData[4][1], out scoreSettings.JigSawPuzzle);
     int.TryParse(stringData[5][1], out scoreSettings.WindowsPuzzle);
     int.TryParse(stringData[6][1], out scoreSettings.Questions);


 }

 private void ReadquestionnaireCSV(string[] data)
 {
     MCQList = new List<MultipleQuestionAnswer>();
     for (int i = 1; i < data.Length; i++)
     {
         string[] fields = data[i].Split(',');
         if (fields.Length <= 1)
         {
         }
         else
         {
             MultipleQuestionAnswer _mtmp = new MultipleQuestionAnswer();
             if (fields[0].Length > 0)
             {
                 _mtmp.Question = fields[0];
                 _mtmp.Answer = new List<string>();
                 if (fields[1].Length > 0)
                 {
                     _mtmp.CorrectAnswer = fields[1];
                     for (int j = 1; j < fields.Length; j++)
                     {
                         _mtmp.Answer.Add(fields[j]);
                     }
                     MCQList.Add(_mtmp);
                 }
             }
         }
     }
 }

 //TODO update score. Writing dummy value for now
 public static void SaveScoreToCsv(Score scoreDetails)
 {
     var csv = new StringBuilder();
     csv.AppendLine(scoreDetails.scoreBreakdown);

     if (Application.platform == RuntimePlatform.WindowsPlayer)
     {
         string path = null;

         if (!CSVReader.generalSettings.useLocal)
         {
             path = CSVReader.generalSettings.configPath + "/Scores.csv";
         }
         else
         {
             int tmpIndex = Application.dataPath.LastIndexOf('/');
             string tmpPath = Application.dataPath.Substring(0, tmpIndex);
             tmpPath += "/Configs/Scores.csv";
             path = tmpPath;
         }

         try
         {
             File.AppendAllText(path, csv.ToString());
         }
         catch (Exception e)
         {
             Debug.Log("Error saving to scores");
         }
     }
 }

 public void ReadGameDescription()
 {
     if (Application.platform == RuntimePlatform.WindowsPlayer)
     {
         var tmpPath = generalSettings.configPath + "Description.txt";

         if (File.Exists(tmpPath))
         {
             ReadDescp(tmpPath);
         }
         else 
         {
             int tmpIndex = Application.dataPath.LastIndexOf('/');
             tmpPath = Application.dataPath.Substring(0, tmpIndex);
             tmpPath += "/Configs/Description.txt";
             generalSettings.useLocal = true;
             if(File.Exists(tmpPath))
                 ReadDescp(tmpPath);
         }
     }
 }

 void ReadDescp(string path) {
     string[] descriptions = System.IO.File.ReadAllLines(path);
     GameDiscription = new GameDiscription();
     GameDiscription.heading = descriptions[0];
     var totalDesc = "";
     for (int i = 1; i < descriptions.Length; i++)
     {
         totalDesc += descriptions[i];
     }
     GameDiscription.description = totalDesc;
 }

 public void PlayBtnClicked()
 {
     HomeScreen.SetActive(false);
     UsernameInputContainer.SetActive(true);
 }

 public void ReadGeneralSetting() {
     if (Application.platform == RuntimePlatform.WindowsPlayer)
     {
         int tmpIndex = Application.dataPath.LastIndexOf('/');
         if (tmpIndex > 0)
         {
             string tmpPath = Application.dataPath.Substring(0, tmpIndex);
             tmpPath += "/Configs/Settings.csv";
             if (File.Exists(tmpPath))
             {
                 string[] descriptions = System.IO.File.ReadAllLines(tmpPath);
                 generalSettings = new GeneralSettings();
                 
                 var desc = descriptions[0].Split(',');
                 int.TryParse(desc[1], out generalSettings.timeOut);

                 desc = descriptions[1].Split(',');
                 desc[1] = desc[1].Replace(@"\", "\\");
                 generalSettings.configPath = desc[1];
                 
                 desc = descriptions[2].Split(',');
                 int.TryParse(desc[1], out generalSettings.lobbyWaitTime);
             }
         }
     }

     if (generalSettings == null)
     {
         generalSettings = new GeneralSettings();
         generalSettings.timeOut = 60;
         generalSettings.configPath = "/Configs/";
         generalSettings.lobbyWaitTime = 100;
         generalSettings.useLocal = true;
     }

     Debug.Log("Config Path: " + generalSettings.configPath);
 }

} Thanks in advance Jash