It would be very helpful if someone anwser this post.. i'm playing arround this filter but I cant use it either cause of this error..
Its been awhile since you posted your question, but I just solved the issue and thought it may still be helpful to you and/or others.
The way UIComponents use spark filters is to clone them, returning a basic flash version of the filter, and add the basic flash version of the filter to the filters list of the superclass DisplayObject. Why they do it this way, I am not sure, but this is how it works.
The reason the spark DisplacementMapFilter doesn't work is because the clone() method does not, well, clone anything. The fix is extremely simple. Subclass the filter and override the clone method and return a flash displacement filter. I suspect this was simply an oversight by the flex devs and since the Displacement filter is so rarely used, no one noticed.
Here is the code for the spark DisplacementMapFilter that works:
public class DisplacementMapFilterFixed extends DisplacementMapFilter
override public function clone():BitmapFilter
return new flash.filters.DisplacementMapFilter(mapBitmap, mapPoint, componentX, componentY, scaleX, scaleY, mode, color, alpha);