Problem with buttons

I’m trying to add actionscript to a button that says:

on (release) {
//Goto Webpage Behavior
getURL(“http://www.thefwa.com?","_blank”);
//End Behavior

}

but when I click the button it won’t let me write any actionscript, it says"current selection cannot have actions applied to it."
I’ve done this before with no problem I don’t know why it won’t let me do it with this button. Any suggestions? Thanks WEich1213