visual effect not working to show stack

[Brahmanathaswami]

I have a main stack and a substack

this button on the main stack is meant to open the substack and show it 
with a visual effect.

It doesn't work... the substack just "snaps" open

LC 6.6.2 OS X Mavericks

on mouseUp

    go invisible stack  "choose date"
    show stack "choose date" with visual effect iris open very slowly

end mouseUp

what am I doing wrong?
-- 
Swasti Astu, Be Well!
Brahmanathaswami

Kauai's Hindu Monastery
www.HimalayanAcademy.com