Serialization problem

I'm writing an object to a file using serialisation. I based it on an
example from the net

public void writeMyObject(){
FileOutputStream fos = null;
ObjectOutputStream out = null;
try
{
fos = new FileOutputStream("test.dat");
out = new ObjectOutputStream(fos);
out.writeObject(myObject);
out.close();
System.out.println("Object Persisted");
}
catch(IOException ex)
{
ex.printStackTrace();
}

myObject class has implements Serializable in its declaration.
What happens is I get a IOException when executing
out.writeObject(myObject);
What may cause this ?, and are there any further tests I can do to find out
the problem ?
Btw the file is created, but not closed properly.
Tony


.