Inconsistent variable behavior... help?

[Mark Swindell]

Here's an example of some odd behavior I'm experiencing in a stack I'm
working on.  On one card the below script works fine and does the desired
behavior.  I switch cards and get the message "can't find card."  Yet the
variables apparently contain correct values on both cards.  I'm stumped.
(The function of the script is to save some user info on a card in a
substack called "defaults.")

A handler at the stack level called from a button:

put field "wordsAvailable" into fld gMyName of grp "WordsAvailableGroup" of
cd gMySound of stack "defaults"

returns "Can't find card."

gMyName = great
gMySound = bay
__