Deserializing data with XML Serializer

Hello, I've a problem with data deserialization. My script is saving data correctly to an XML file but I cannot load anything from it, since XmlSerializer is returning bug, which says:

 InvalidCastException: Value is not a convertible object:

Here is my script:

   public void Save() //Saving data to XML file
     {
         var serializer = new XmlSerializer(typeof(GroundContainer));
         using (FileStream stream = File.Create(Application.persistentDataPath + "/groundSaveData.xml"))
         {
             GroundContainer data = new GroundContainer();
             data.AddingGrounds();
             serializer.Serialize(stream, data);
         }
     }
 
     public void Load() //Loading data from XML file
     {
         if (File.Exists(Application.persistentDataPath + "/groundSaveData.xml"))
         {
             var serializer = new XmlSerializer(typeof(GroundContainer));
             FileStream stream = File.Open(Application.persistentDataPath + "/groundSaveData.xml", FileMode.Open);
             //Problems occurs in this place
             var container = (GroundContainer)serializer.Deserialize(stream) as GroundContainer;
             stream.Close(); 
         }
     }
 }
 
 [Serializable]
 public class Ground
 {
     [XmlAttribute("groundName")]
     public string name;
 
     [XmlAttribute("position")]
     public Vector3 position;
 
     [XmlAttribute("sprite")]
     public Sprite sprite;
 }
 
 [XmlInclude(typeof(Vector3))]
 [XmlInclude(typeof(Ground))]
 [Serializable]
 [XmlRoot("GroundCollection")]
 public class GroundContainer
 {
 
     [XmlArray("Grounds")]
     [XmlArrayItem("Tile")]
     public List<Ground> grounds = new List<Ground>();
 
     public void AddingGrounds()
     {
         GameObject[] groundTiles = GameObject.FindGameObjectsWithTag("Ground");
         for (int i = 0; i < groundTiles.Length; i++)
         {
             Ground toAdd = new Ground();
             toAdd.name = groundTiles[i].name;
             toAdd.position = groundTiles[i].transform.position;
             toAdd.sprite = groundTiles[i].GetComponent<SpriteRenderer>().sprite;
             grounds.Add(toAdd);
         }
     }
 }

Add here is fragment of the data from XML file:

 <?xml version="1.0" encoding="windows-1250"?>
 <GroundCollection xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
   <Grounds>
     <Tile groundName="Ground" position="(0.0, -1.0, 0.0)" sprite="ColorSheet_34 (UnityEngine.Sprite)" />
     <Tile groundName="Ground(Clone)" position="(9.0, -1.0, 0.0)" sprite="ColorSheet_34 (UnityEngine.Sprite)" />
     <Tile groundName="Ground(Clone)" position="(10.0, -1.0, 0.0)" sprite="ColorSheet_34 (UnityEngine.Sprite)" />
     <Tile groundName="Ground(Clone)" position="(11.0, -1.0, 0.0)" sprite="ColorSheet_34 (UnityEngine.Sprite)" />
     <Tile groundName="Ground(Clone)" position="(12.0, -1.0, 0.0)" sprite="ColorSheet_34 (UnityEngine.Sprite)" />
   </Grounds>
 </GroundCollection>