What does "SerializationException: Unexpected binary element: 116" mean?

This happened after I shrunk down my script to just one function for refreshing the saved data. The Unity Console doesn't give me any error after I saved the script. This issue shows up when I run my app in Unity. I tried to change the script execution order, but no luck either. I copied the code from my previous script; it worked fine recently.

 using System.Collections;
 using UnityEngine;
 using System.IO;
 using System.Runtime.Serialization.Formatters.Binary;
 
 public class UserInfo : MonoBehaviour {
 
     public string _UserName;
     public ArrayList SavedGamerID;
     public string ServerName;
 
     void Start(){
 
 
         this.gameObject.GetComponent<DownloadAndUpLoadUserData>().DownloadLocalUserData();
 
         RefreshSavedUserInfo();
 
     }
 
 
     public void RefreshSavedUserInfo() {
 
 
         if (File.Exists(Application.persistentDataPath + "/UserInfo/UserAccount.save"))
         {
 
             BinaryFormatter bf = new BinaryFormatter();
             FileStream file = File.Open(Application.persistentDataPath + "/UserInfo/UserAccount.save", FileMode.Open);
             UserData data = (UserData)bf.Deserialize(file);
 
             _UserName = data.UserName;
             SavedGamerID = new ArrayList(data.GamerInfo);
             
 
             file.Close();
 
         }
 
     }
 
     public void SaveUserInfo() {
 
         FileStream file;
 
         BinaryFormatter bf = new BinaryFormatter();
         file = File.Create(Application.persistentDataPath + "/UserInfo/UserAccount.save");
         UserData data = new UserData();
 
         data.UserName = _UserName;
         data.GamerInfo = new ArrayList(SavedGamerID);
 
         bf.Serialize(file, data);
 
         RefreshSavedUserInfo();
     }
 
 }
 

[1]: /storage/temp/100599-capture.png