Példa

public static class SerializableObject implements Serializable{

synchronized private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
s.defaultReadObject();
}
}

Megoldás
A readObject() metódust synchronized módosító nélkül deklarálja

public static class SerializableObject implements Serializable{

private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
s.defaultReadObject();
}
}