Invisible Button: God I Hate This

It just doesn't make any sense. I'm doing exactly what I did in other projects, but for some reason I get the following error message:

**Error** Scene=Scene 1, layer=saigon button, frame=1:Line 1: Mouse events are permitted only for button instances
on(press){

... But it IS a stinking button instance! I made the little rectangle, converted it to a button symbol, inserted it into a new layer over a photo and applied the following AS to the keyframe/symbol:

on(press){
getURL("photo_gallery_saigon.htm","_self")
}

I've done EXACTLY the same thing I did on a couple of other projects; yet the error appears on publishing. The properties tab reads, "Instance of: Button Saigon." So how does the error message come to say it's not a button instance?! I've also tried it with "on(release){", and I've tried making the photo into a button symbol.

I can understand that the program is very persnickety about details, but it drives me up the frigging wall when something makes no sense. Can anybody suggest a solution? Please?

Because you have that code on the timeline as well, probably by accident.