Moving canvas item's to new canvas not working

[The Surprises <thesurprises1 attbi com>]

I am trying to move gnome_canvas_item's from one canvas to another.  I
am using gnome_canvas_item_reparent, and giving it the item to move, and
the new canvas's root, like this:

gnome_canvas_item_reparent (clip_box, gnome_canvas_root(GNOME_CAVAS(new_canvas));

I get the following error when I try this:

GnomeUI-CRITICAL **: file gnome-canvas.c: line 1280 (gnome_canvas_item_reparent): assertion `item->canvas == GNOME_CANVAS_ITEM (new_group)->canvas' failed.

It's not liking the reparenting for some reason but I'm not getting it.
Any ideas?

Thanks
Jason