Locked Stack Error Message II

[Rob Cozens]

>Where/how is the stack locked, and how do I unlock it?

PS: I know I can fix this particular problem by deleting and 
recreating the group's field; but I want to understand where the lock 
is coming from.
-- 

Rob Cozens
CCW, Serendipity Software Company
http://www.oenolog.com/who.htm

"And I, which was two fooles, do so grow three;
Who are a little wise, the best fooles bee."

from "The Triple Foole" by John Donne (1572-1631)