Android :: Google Maps Itemized Modification Exception

I cannot figure out the origin of the ConcurrentModificationException. In my activity I'm calling
updateMapOverlay(). I'm also calling updateMapOverlay() inside another Thread (a TimerTask) that is invoked on regular intervals. I'm taking the appropriate locks when invoking updateMapOverlay() from both the threads. Is this problem being caused because I'm invoking updateMapOverlay from inside a non-UI thread (i.e., TimerTask).

private void updateMapOverlay() { this.itemizedOverlay.refreshItems(createOverlayItemsList());
List<Overlay> overlays = mapView.getOverlays(); overlays.clear();
overlays.add(cotItemizedOverlay); this.mapview.invalidate(); }

Exception:
W/dalvikvm(10641): threadid=3: thread exiting with uncaught exception (group=0x4001b180)
E/AndroidRuntime(10641): Uncaught handler: thread main exiting due to uncaught exception
E/AndroidRuntime(10641): java.util.ConcurrentModificationException....