"Can't set property" returned upon trying to set the hScroll, vScroll of a group from card script

[Jessica McBeck]

Hi all,

I am attempting to set the hScroll and vScroll of a group from a card's
script. This card does not contain the group. Here's the script:

set the vScroll of group "ScrollingGroup" of card this_Card of stack
this_Stack to y
set the hScroll of group "ScrollingGroup" of card this_Card of stack
this_Stack to x

But during runtime livecode returns the error "Can't set property".
However, when I place a button on this_Card with the script

on mouseDown
   put the vScroll of group "ScrollingGroup" into v
   add 10 to v
   set the vScroll of group "ScrollingGroup" to v
end mouseDown

the group scrolls as expected. So then I tried calling a "send" command to
the button from the card script with the necessary scroll values and got
the same "Can't set property" error message. Here's that code:

In the card this_Card script:

send "scrollMe" && x_b & comma && y_b to button "set scroll"

In the button "set scroll" script:

on scrollMe scrollX, scrollY
   set the vScroll of group "ScrollingGroup" to scrollX
   set the hScroll of group "ScrollingGroup" to scrollY
end scrollMe

I imagine the problem is related to the linear flow of the message path,
but cannot think of a clever work-around. Any suggestions are greatly
appreciated!

Thanks,
Jess