I had the same error as vicky49.
In my case I use a tree as an Explorer to cut and paste nodes with drag and drop.
Example:
<ice:panelGroup scrollHeight="500px" id="scroll_id">
<ice:tree ...
<ice:treeNode>
...
<ice:panelGroup draggable="true"
dropTarget="true"
dropTargetScrollerId="scroll_id"
...
>
...
</ice:panelGroup>
</ice:treeNode>
</ice:tree>
</ice:panelGroup>

The tree is located, as shown above, in a Scrollable Div. The scroll bars will be shown, if the nodes are expanded. In order to drop a node in another unseen node you have to scroll the area. Actually you can only do it with the arrow keys. An autoscroll is not implemented.

After copious research, I found the "scroll" attribute in the Draggable function in the script.aculo.us framework. This enables the auto scroll function using drag and drop. If a node is hovered over the bottom of the Scrollable Div, the area is automatically scrolled down.

In order to add this feature, I changed the GroupRenderer.java and DragDrop.java class and used 'dropTargetScrollerId' as scroll id.
I overloaded the DragDrop.addDragable and called them in the GroupRenderer as you can see in the following lines:

String scrollid = (String) uiComponent.getAttributes().get("dropTargetScrollerId");
            if (scrollid != null && scrollid.trim().length() > 0) {
                calls += DragDrop.addDragable(uiComponent, uiComponent.getClientId(facesContext), handleId,
                        dragOptions, dragMask, facesContext);
            } else {
                calls += DragDrop.addDragable(uiComponent.getClientId(facesContext), handleId, dragOptions, dragMask,
                        facesContext);
            }

In the DragDrop class I get the correct part of the id:
String scrollid = (String) uiComponent.getAttributes().get("dropTargetScrollerId");
        if (scrollid != null && scrollid.trim().length() > 0) {
            UIComponent scroller = D2DViewHandler.findComponentInView(facesContext.getViewRoot(), scrollid);
            if (scroller != null) {
                scrollid = scroller.getClientId(facesContext);
            }
        }

And add the id as an attribute to the JavaScript function:
if (scrollid != null && scrollid.trim().length() > 0) {
            ea.add("scroll", scrollid);
        }

Could you implement a similar feature in the next version, please?
In version 2.0 it is also not implemented.