im getting a serialization exception eror in my load method

 using System.Runtime.Serialization.Formatters.Binary;
 using UnityEngine;
 using System.IO;

 public static class SaveSystem
 {
     public static void SaveData(Calculator calculator)
     {
     BinaryFormatter formatter = new BinaryFormatter();
     string path = Application.persistentDataPath + "Alma3Gold.formula";
     FileStream stream = new FileStream(path, FileMode.Create);

     Data data = new Data(calculator);

     formatter.Serialize(stream, data);
 }

 public static Data LoadData(Calculator calculator)
 {
     string path = Application.persistentDataPath + "Alma3Gold.formula";
     Data data = new Data(calculator);

     if (File.Exists(path))
     {
         BinaryFormatter formatter = new BinaryFormatter();
         FileStream stream = new FileStream(path, FileMode.Open);

         data = formatter.Deserialize(stream) as Data;
         stream.Close();
     }
     else
     {
         Debug.Log("Save file not found in " + path);

         data.PRICE = 0;
     }

     return data;
 }

}