This NotSerializableException is thrown because you tried to serialize an
object of type WToolkit. By default serialization writes out all non-static
and non-transient member variables. Therefore I would guess that you have a
member variable of type Toolkit declared somewhere in your class. The
solution would be to change your declaration from for example
   private Toolkit toolkit;
to
   private transient Toolkit toolkit;
Of course then you would have to set your toolkit variable during
deserialization in another way, probably in a readObject() method. For how
to declare and implement this method,  see
<http://java.sun.com/j2se/1.4.2/docs/api/java/io/Serializable.html> and
<http://java.sun.com/developer/technicalArticles/Programming/serialization/index.html>.