Unity crashing when serializing a list using XML

Unity keeps crashing when I want to serialize a list of some object. I thought it might be because Vectors are not seralizable but after creating a custom class to handle that problem it still crashes. The part where it crashes is when I call the serialization. Right now I have

Custom object to handle vectors

 public struct HmSerilizer{
             public float x,y,height;
             public HmSerilizer(float a, float b, float c){
                 x = a;
                 y = b;
                 height = c;
             }
         }

List

 [XmlArray("Heights"),XmlArrayItem("Height")]
     public List<HmSerilizer> hmList{
         get{
         for(x = 0; x < hmWidth; x++){
             for(y = 0; y < hmHeight; y++){
                 hmList.Add(new HmSerilizer(x,y,hm[x,y]));
                 }
             }
             return hmList;
         }
         set{        
             hm = new float[hmWidth,hmHeight];
             for(x = 0; x < hmList.Count;x++){
                 hm[(int)hmList[x].x,(int)hmList[x].y] = hmList[x].height;
             }
         }
     }

XML saving part

 public void Save(){
     FileStream fs = new FileStream("C:\\Users\\Borzen\\Desktop\\save.xml",FileMode.Create);
     XmlSerializer xs = new XmlSerializer(typeof(SFField));
     xs.Serialize(fs,this);
     fs.Close();
 }

let me know if I can be of any help to try to solve this problem.