[flexcoders] Error #1009 - Problem running swf on production server

[sarah_e_boys]

I get the following error when I try and run my application on a 
production server:

TypeError: Error #1009: Cannot access a property or method of a null 
object reference.
        at samples::MyTreeItemRenderer/set data()


The application works fine if I reference it with http://localhost or 
run if from Flex Builder. I hope it is something very simple regarding 
a reference to the MyTreeItemRenderer.as class not being compiled into 
the swf file.  I would be grateful for any suggestions...