Error #1030: Stack depth is unbalanced

I've got this strange problem where this code:

private function initLevel():void {
    var levelMap:Array = 
    [ 
           [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
           [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
    ];
    for (var y:* in levelMap) {
        for (var x:* in levelMap[y]) {
            trace(y, x);
            trace(levelMap[y, x]);
        }
    }
}

produces this ugly monster in flashdevelop:

typecheck Level/initLevel()
  outer-scope = [global Object$ flash.events::EventDispatcher$ flash.display::DisplayObject$ flash.display::InteractiveObject$ flash.display::DisplayObjectContainer$ flash.display::Sprite$ flash.display::MovieClip$ Level$]
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {} ()
  0:debugfile "L:\svntest\flashgame\src;com\thom\TD;Level.as"
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {} ()
  2:debugline 66
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {} ()
  4:getlocal0
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {} (Level[O])
  5:pushscope
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {Level[O]} ()
  6:pushundefined
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {Level[O]} (void[A])
  7:coerce_a
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {Level[O]} (*[A])
  8:setlocal2
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {Level[O]} ()
  9:pushundefined
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {Level[O]} (void[A])
  10:coerce_a
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {Level[O]} (*[A])
  11:setlocal3
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {Level[O]} ()
  12:debug
                       [Level[O] *[A] *[A] *[A] *[A] *[A] *[A] *[A]] {Level[O]} ()
  17:debug
                       [L