Illegal CrossThread Invalid Operation Exception On Form.Invoke()

Got a proccess thread thats in charge of loading a listbox full of the first line of text for richtextbox items on form load. Though I use Me.Invoke(New MethodInvoker...) to add items on the main thread so its thread safe it coughs when the first line of rtf data are thrown at it, acting as if I hadnt called adding the items on the main thread.

Up at the class level:
Dim Worker As System.Threading.Thread
In the load procedure for the form:
Worker = New System.Threading.Thread(AddressOf WorkerDo)
Worker.Start()

[Code]....

I"ve also tried to remedy this using a delegate to invoke the listbox before attempting to update it, but the invoke method itself is throwing the exception. I am not using the default instance of the form (a new instance of this form is created). Anyone know how I can get around this? I can't load the listbox full of items directly in the form's load procedure because work takes place in the thread beforehand so there are strings to add to the listbox. I've got MS Visual Studio 2008 Pro and Vista SP2 (latest updates applied).