I answer easy ones.
> I am also getting the following error within eclipse in the Add.Java file:
> public class Add extends GPNode....The serializable class Add does not
> declare a static final serialVersionUID field of type long
Add following line for "Add" class.

private static final long serialVersionUID = 1L;

> Could someone please help me to understand why this is occurring.

Eclipse has possibility define more varnings on or off, often warning level 
things are not severe mostly just anonying in big projects.
If you use several different JDK:s example both linux and windows 
enviroments to previous warning is more important than using only on JDK in 
enviroment that calculates default seralVersionUID right.

t. Harri

> Sincerely,
> Gerard
> I have not included the libraries list since I believe this is 
> unnecessary.