vertical background moving

Hi, i want to make my background move vertically seamlessly.

I did search the forum but it's no help including the tutorial examples which are more for horizontal background which i dont understand how to apply to vertical.

I can't post the my file because of my artwork but here's what i used.

Condition: Y > -self.height/2

action:     Self.y - Self.height / 2

+Every Tick

-Set Y to Self.Y-60*dt

not working?

Here's the capx file - sendspace.com/file/9ivj7v

I have a bg that is a double image which can loop seamless

Any help is appreciated!

i just figure out of 'tiled background' but it is still so confusing to use it vertically.. anyone has a vertical example??

bump..

got any help??

am also stuck over here...