NullPointerException thrown when generating SWING GUI

Hi there folks,
I am currently writing a small application that is used to demonstrate multi threading in a Swing-based interface application.
The Main method initialises an array of objects, a couple of DefaultListModels with another set of assigned objects.
I have then passed these parameters to an instance of another type of GUI class, generated by a simple new() GUIClass call, which incedentally initialises aand displays without exception.
When I try to genrate an instance of the same GUI class from a JButton event in the calling class, I have a NULLPOINTEREXCEPTION thrown. Signs presently indicate that it is being thrown by the parameters passed into the called GUI class.
I have become a little frustrated as I have been able to generate printlyn lists of the contents of the array, DefaultListModels from both the calling GUI class and the called GUI class.
I am at a loss presently and would appreciate some possible pointers, excuse the pun, to any possible solutions.

Hi Martin,
Welcome to JavaRanch. Without seeing some code and the stack trace of the NPE, it's going tough for us to help out. Try posting some code and the stack trace.