Animation will only play once

Hey,
I have the following code that brings in a movie animation. My problem is that once the animation is finished and the user presses the ‘back’ button to navigate elsewhere on the website, if they go back to the animation and click the ‘great_btn’ the animation won’t play again.

_root.main_cntr.btns_mc.great_btn.onRelease = function() {
 loadscrollIt();//on release of the great lengths button the function 'loadscrollit' is called
 disableBtns(btnArray);
 _root.homepage_cntr._alpha = 0;//sets homepage_cntr to 0 so containers below it can be ssen
 _root.photos_cntr._alpha = 0;//sets photos_cntr to 0 so containers below it can be seen
 _root.btns_cntr.alphaTo(0,1,"easeOutCubic");//fades btns_cntr to 0 with an ease so containers below it can be seen
 _root.main_cntr.main_txt.alphaTo(0,.4,"easeOutCubic")//fades the main_txt found in the main_cntr to 0 with an ease
 _root.sub_cntr.main_txt.alphaTo(0,.4,"easeOutCubic")//fades the main_txt found in the sub_cntr to 0 with an ease
 _root.main_cntr.sub_txt.alphaTo(0,.4,"easeOutCubic")//fades the sub_txt found in the main_cntr to 0 with an ease
 _root.sub_cntr.sub_txt.alphaTo(0,.4,"easeOutCubic")//fades the sub_txt found in the sub_cntr to 0 with an ease
 _root.main_cntr.btns_mc.alphaTo(0,1,"easeOutCubic")//fades the btns_mc found in the main_cntr to 0 with an ease
 _root.great_cntr.loadMovie("great_lengths.swf");//loads the movie "great_lengths" into the great_cntr
 _root.pattern_cntr1.background1.alphaTo(25,0.8,"easeOutCubic",0.5);//fades the background to 25% with an ease
 _root.pattern_cntr2.background2.alphaTo(25,0.8,"easeOutCubic",0.5);
 _root.main_cntr.back_btn1.alphaTo(100,1,"easeOutCubic",24)//fades the back_btn1 to 100 with an ease and a delay of 24 seconds so that it appears at the end of the great lengths animation
 } 

I tried adding this line of code to the back_btn so that the animation is actually loaded in on every click of ‘great_btn’ but it’s not working.

_root.great_cntr.unloadMovie("great_lengths.swf");

Any ideas?
Cx