I'm having trouble masking LoadedMovies dynamically

Currently i load the image into an empty movie clip and the mask into another empty movie clip as follows:

code:


_root["container"+n].createEmptyMovieClip("image"+i, this.getNextHighestDepth());		

_root["container"+n]["image"+i].createEmptyMovieClip("mcontainer"+i, this.getNextHighestDepth());

_root["container"+n]["image"+i]["mcontainer" + i].attachMovie("mask", "mask" +i, this.getNextHighestDepth());


I then load an image into the image movie clip and try to apply the mask to it as follows:
code:


_root["container"+n]["image" + i].loadMovie(imageurl)

_root["container"+n]["image" + i].cacheAsBitmap = true; 

_root["container"+n]["image" + i].setMask(_root["container"+n]["image" + i]["mcontainer"+i]["mask"+i]);


(the I / N values are because they are in a loop )

Can anyone offer any advice, am so close to finishing this project and this is the final hurdle!