Understanding failed assertions

[Vikram Noel Ambrose <noel ambrose gmail com>]

Hello everyone,

I'm relatively new to GTK. I'm trying to understand the Drag-and-Drop 
mechanism for Treeviews. Here is my sample program: 
http://en.pastebin.ca/1719087

The sample code can be compiled as is and run without modification.

gcc -g `pkg-config --cflags --libs gtk+-2.0`  -o dnd dnd.c

When I click and drag a row from the left treeview and drop it into the 
right hand side treeview, I get the following messages duplicated 4 times.

----------
(dnd:21965): Gtk-CRITICAL **: gtk_list_store_get_value: assertion 
`VALID_ITER (iter, list_store)' failed

(dnd:21965): GLib-GObject-CRITICAL **: g_strdup_value_contents: 
assertion `G_IS_VALUE (value)' failed

(dnd:21965): GLib-GObject-CRITICAL **: g_value_unset: assertion 
`G_IS_VALUE (value)' failed
----------

Obviously the sample program is not functionally complete, but I cannot 
understand what causes these messages and how to rectify the problem.

Does anyone know whats going on?

thanks,

Vikram.