Save and Load Problem, Dont quite understand.

Hi, I have a problem.

I cant work out why I cant seem to load and unload a class with three lists in it.

It keeps giving me this cast error:

InvalidCastException: Cannot cast from source type to destination type. EndlessManagerScript.LoadChunk (Vector3 fileNamePos) (at Assets/GAME ASSETS/SCRIPTS/EndlessManagerScript.cs:298) PlayerControlScript.Update () (at Assets/_CUSTOM ASSETS/SCRIPTS/PlayerControlScript.cs:204)

My class is:

  [Serializable]
 public  class blockData  
     {
 
         public List<string> objectNamesToSerialize = new List<string>();
         public List<Int32> xPosToSerialize = new List<Int32>();
         public List<Int32> yPosToSerialize = new List<Int32>();
 
     }

My save method is:

           try
             {
 
                 Stream stream = File.Open(Application.dataPath + @"\Saves\Chunks\chunk " +  thisChunkFilenameNumber, FileMode.CreateNew);
                 BinaryFormatter bformatter = new BinaryFormatter();
 
                    data.objectNamesToSerialize = objectNamesToSerialize;
                     data.xPosToSerialize = xPosToSerialize;
                     data.yPosToSerialize = yPosToSerialize;
 
                     
                
                 bformatter.Serialize(stream, data);
                 stream.Close();
 
             }
             catch (UnauthorizedAccessException) { print("SAVING ERROR!!!"); } //many more exception might happen, check documentation
      
              }

And my loading script is just:

  public  void LoadChunk(Vector3 fileNamePos)
     {  
         
             
             {
                 Stream stream = new FileStream(Application.dataPath + @"\Saves\Chunks\chunk " + fileNamePos, FileMode.Open,FileAccess.Read);
                 
                BinaryFormatter bformatter = new BinaryFormatter();
 
                  data = new blockData();
  
        data.objectNamesToSerialize = ((List<string>) bformatter.Deserialize(stream));
 
             //  here is where I've tried lots of different ways of reading it, i even mucked around with 
             //  binaryReader and had the same problems.  It cant seem to cast back into a new
             //  instance of the blockdata class for some reason.
 
 
                   stream.Close();
                   print(data.objectNamesToSerialize.Count);
             
                 File.Delete(Application.dataPath + @"\Saves\Chunks\chunk " + fileNamePos);
              
             }
             }

Not sure what I'm doing wrong. Thought I'd be able to save a list and then reload the list as is. Could anyone help me please?