Is there an upper bound to the size of a sprite in as3 / flash 10?
I know bitmapData has limitations...
Back2dos' post seems very informative, but just watch out if you are caching as a bitmap (DisplayObject.cacheAsBitmap = true, applying a BitmapFilter will also cause this), as you will then be limited by flash's bitmap size limit.
DisplayObject.cacheAsBitmap = true
BitmapFilter