Seems there’s an error in the script for the ZB4 version of paintstop, it can’t ifnd the lightbox.
Error is : ZScript Node: Interface item could not be found. Texture:TurnOnLightBox in… [IGet, Texture:TurnOnLightbox]
This stops the script from running. Using ZB 4 on Windows 7 (64).
Yeah, happens on the mac too.
They posted a response in the main forum that a fixed plug would be posted soon.
Just a heads up. 
Please post in the appropriate forum (each plugin has its own thread) such as this one:http://www.zbrushcentral.com/showthread.php?t=91897
visit: http://www.zbrushcentral.com/forumdisplay.php?f=70
Thank you.