Serialization scripting error

The modified script I am using to save, load and deletes saves of my game gives the error "Unknown identifier Convert" on line 73, could someone help me fix this?

 import UnityEngine;
 import System.Collections;
 import System.Collections.Generic;
 import System.Linq;
 import Serialization;
 import System.Reflection;
 import System.IO.Compression;
 import System.IO;
 import System.Net;
 import System.Collections.Generic;
 
 var paused : boolean = false; 
 var pausedGUI : GUITexture;  
 var gameName : String = "Your Game";
 
 var myList = new List.<Transform>();
 
 function Start()
 {
     if(pausedGUI)
         pausedGUI.enabled = false;
 }
 
 function Update () 
 { 
     if(Input.GetKeyUp(KeyCode.Escape))
     { 
        paused = !paused;
 
         if(paused == true){
             Time.timeScale = 0.0;
             if(pausedGUI) pausedGUI.enabled = true;
         } else {
             Time.timeScale = 1.0;
             if(pausedGUI) pausedGUI.enabled = false;
         }
    }
 }
 
 function OnGUI() {
     if(!paused)
     {
        GUILayout.BeginArea(Rect(200,10,400,20));
        GUILayout.BeginVertical();
        GUILayout.BeginHorizontal();
        GUILayout.FlexibleSpace();
        GUILayout.FlexibleSpace();
        GUILayout.EndHorizontal();
        GUILayout.EndVertical();
        GUILayout.EndArea();
        return;
     }
        
     var box : GUIStyle = "box";   
     GUILayout.BeginArea(Rect( Screen.width/2 - 200,Screen.height/2 - 300, 400, 600), box);
 
     GUILayout.BeginVertical(); 
     GUILayout.FlexibleSpace();
     if(GUILayout.Button("Save Game"))
     {
        LevelSerializer.SaveGame(gameName);
     }
     
    
     
     GUILayout.Space(60);
     for(var sg in LevelSerializer.SavedGames[LevelSerializer.PlayerName]) {
     
     if(GUILayout.Button("Deletes Save"))
     {
     LevelSerializer.SavedGames[LevelSerializer.PlayerName].Remove(sg);
     
     var data = Convert.ToBase64String(UnitySerializer.Serialize(LevelSerializer.SavedGames));
     data.WriteToFile(Application.persistentDataPath + "/saves");
     break;
     }
     
        if(GUILayout.Button(sg.Caption)) {
          LevelSerializer.LoadNow(sg.Data);
          Time.timeScale = 1;
          }
     } 
     GUILayout.FlexibleSpace();
     GUILayout.EndVertical();
     GUILayout.EndArea();
 
 
 }