WebGL XML parsing error "InvalidOperationException"

 "InvalidOperationException: The specified type was not recognized: name='DialogueObjective' namespace=", at <Objective xmlns=">"

I am using XMLSerializer to save and load data for a quest system. I am able to handle the extra types and the parsing works in all builds, except in WebGL. When I book up WebGL, I get this error. DialogueObjective is a derivative of the Objective class. Here is the XML line in question:

 <Objective xsi:type="DialogueObjective">

Objectives are contained in a list inside of a class "Quest". Quest is serialized and Deserialized and handed an array of Types derived from Objective. This works in editor and all other build types, EXCEPT in WebGL

Here is the serialization code for Quest:

 public static Quest SaveData(string path, Quest q = null){
 
         if(q == null){
             q = new Quest();
             q.Objectives.Add(new InteractObjective());
         }
 
         XmlSerializer questSerializer = new XmlSerializer(typeof(Quest), GetClasses(typeof(Objective)).ToArray());
 
         using(var stream = new FileStream(path, FileMode.Create)){
             questSerializer.Serialize(stream,q);
         }
 
         return q;
 
     }
 
     public static List<System.Type> GetClasses(System.Type baseType){
         return System.Reflection.Assembly.GetCallingAssembly().GetTypes().Where(type => type.IsSubclassOf(baseType)).ToList();
     }
 
     public static Quest Load(string data){
 
         XmlSerializer serializer = new XmlSerializer(typeof(Quest), GetClasses(typeof(Objective)).ToArray());
         return (Quest)serializer.Deserialize(new StringReader(data));
 
     }