Mc on button command

Can someone help me out Im not a programmer.
I placed a movie clip in the over state of a button
when I go to add the script, "on (release) {
gotoAndPlay(“Scene 3”, “pub”);
} the button acts funny, sometimes it works and other
times it takes me to another scene or loops the whole swf.
Should I putting a preloader in each scene or on the button?