I don't believe that the error is caused by code created by the GUI Builder but some explanation on how G4P handles events might help you pin-point the problem.

At the time a control is created (using new keyword) G4P will look for a particlar event handler method in your sketch. For a GButton it will look for the method

1. public void handleButtonEvents(GButton button, GEvent event){
2.    // handler code
3. }

If it can't find the method then it will display a warning about the event handler being found. You have three options

1. Add the method above to your sketch,
2. Add your own event handler,
3. Ignore it, the sketch will run but the control won't work (not much point in having the control ).

Most novices will go for (1) since you can simply copy and paste the empty method from the warning message into the sketch (saves remembering it )

Option (2) is a possibility but if you are using the GUI Builder tool it will create the code for you. The advantage of using GUI Builder is that the GUI creation code will have the correct syntax and will work. In this case you can disable the default warning messages with

1. G4P.messagesEnabled(false);

place this in the setup method before calling the createGUI method.

G4P uses Java Refeflection to call the event handlers and if an exception occurs inside a handler the stack trace (the highlighted stuff in your post) will include a line including words about invoking methods.

GUI Builder adds the gui tab to your sketch and I stress that the user must be careful in editing the code in this tab. User defined methods should not be added to this tab, place them in your main sketch tab, code should ONLY be added inside the eventhandler methods and the control creation code must NOT be edited.

HTH

Is that done by standard unless you disable the messages?

Yes the warning is created when the control is created but the custom event handler can only be specified once the control is made, so use the following statement before creating any controls.

1. G4P.messagesEnabled(false);

Sorry to make you go into all that detail.

No problem, this library has many features and the more you understand about the workings of G4P the more you will get out of it.