Menu tutorial

hey i was wonderin about that 1 tutorial (http://www.kirupa.com/developer/mx/dropdownmenu.htm)
on the part where your supposed to ut in
“on(rollOver){
gotoAndStop(“open”)
}”
this is the error i come up with:
“Symbol=Menu, Layer=Buttons, Frame=1: Line 1: Mouse events are permitted only for button instances
on(rollOver) {”
what am i doing wrong?(as you can tell im new with flash) any suggestions would be greatly appriciated

thanks