Blur filter in class file

1

I am using

var blurFilter:Array = this_mc.filters;
blurFilter[0].blurX = 10;
this_mc.filters = blurFilter;

to induce a 10px blur on my MC. It works when the code is placed right on the timeline of the MC in question.

However when i use the exact same code in an external “effects” class file, it does not work.

Should i be looking at refferencing problems? Scoping problems? What gives?