Change stack in openStack

[David Vaughan]

Hi

In accord with advice on the web site, I have a sub-stack which contains 
data to be saved between runs of the application. When opening the main 
stack, I want to retrieve some defaults and last user data and populate 
the main stack fields. This is a fragment of the code:

on openStack
   global gPinions, gSpurs
   set hilite of button "Pinion" to false
[more "set" statements deleted]
   set hilite of button "Rollout" to true
   put empty into field "poss rollout"
   put 0.5 into field "Tolerance"
   lock screen
   go stack "Gears"
[more lines deleted]
end openStack

I tried painfully building the lines until I could isolate where it fell 
over, as the debugger seems arcane. It is when you add the code
  <<go stack "Gears">> when it produces this error, apparently from one 
of the tool stacks, not mine. This is the message:
==============
  • There was an Execution Error at 9:30:23 PM
Error description:  if-then: error in statement
Revolution User Interface Error: Object: button id 1137 of group id 1136 
of card id 1002 of stack 
"/Elsewhere/Users/davidv/Applications/Revolution 1.1 OS 
X/components/tools/revmenubar.rev"
--------------------
if it is not empty then
--------------------
Value: menuPick
===============

The same code works perfectly if I put it in a button and execute it 
"manually".
What is going on here please?

thanks
David Vaughan