External file's AS problem

I’m using the belwo AS to trigger my rollover and rollout animations for a button in an mc. My buttons are in a seperate swf file and I am importing them using a container method into my main layout but when I rollover and rollout nothing is happening yet the animations work when the imported file is viewed alone, any reasons why?

[AS]this.about_mc.about_butt.onRollOver = function(){
this.about_mc.about_butt.onRollOut = function(){

Thanks for your time