XML Serialization problem

I'm getting the following error:

InvalidOperationException: To be XML serializable, types which inherit from IEnumerable must have an implementation of Add(System.Object) at all levels of their inheritance hierarchy. UnityEngine.Transform does not implement Add(System.Object).

Here's my code:

     using UnityEngine;
     using System.Collections;
     using System.Collections.Generic;
     using System.Xml;
     using System.Xml.Serialization;
     using System.IO;
     using System.Text;
     
     [XmlRoot("world")]
     public class WorldContainer
     {
         [XmlArray("tile"),XmlArrayItem("item")]
         public Tile[] tiles;
         
         //load XML file
         public static WorldContainer Load(string path)
         {
    ------->     var serializer = new XmlSerializer(typeof(WorldContainer));
             using(var stream = new FileStream(path, FileMode.Open))
             {
                 return serializer.Deserialize(stream) as WorldContainer;
             }
         }
         
     }

I read thorugh some other answers on here that the class to be serialized cannot inherit the MonoBehavior class, mine doesn't. Any help is greatly appreciated