SerializationException: serializationStream supports seeking, but its length is 0

I'm trying to save some user data, when I first save the file is created but when attempt to load from it the I get the "SerializationException: serializationStream supports seeking, but its length is 0" error

    if (File.Exists(Application.persistentDataPath + "/IDlist.dat"))
         {
             int temp=0;
             int id;
             int max=0;
             BinaryFormatter bf = new BinaryFormatter();// file open
             FileStream file =  File.Open(Application.persistentDataPath + "/IDlist.dat", FileMode.Open);
             ID data;
             data= (ID)bf.Deserialize(file);//issue with this here 
           
             for(int i=0; i< data.userID.Length; i++)
             {
                 temp = data.userID[i];
                 max = i;// find max id count
             }
             id = temp+1;
             data.userID[max+1] = id;// store new id
             bf.Serialize(file, data);
             file.Close();
             CreateUser(id);// send id
 
         }// if users exist 
         else
         {
             
             BinaryFormatter bf = new BinaryFormatter();
             FileStream file = File.Create(Application.persistentDataPath + "/IdList.dat");
             ID data= new ID();
             data.userID.Initialize();
             data.userID[0] = 0;
             bf.Serialize(file, data);
             file.Close();
             CreateUser(0);
         }

I've looked around but I can't find anything relevant to help me