GtkTree, cell with toggle

[p s <tuxnduke welho com>]

I have created a table with GtkTree and on one colums I have a chechbox 
to indicate certain boolean value... All in all the tree works ok, 
renders properly and I have sortable/clickable headers in the table and 
that too works. I experience a problem on a callback where the checkbox 
is clicked..

currently I have:

static GtkTreeView * tree;
static GtkTreeStore *store;
...

store = gtk_tree_store_new (N_COLUMNS,
                                G_TYPE_INT,
                                G_TYPE_STRING,
                                G_TYPE_STRING,
                                G_TYPE_INT,
                                G_TYPE_STRING,
                                G_TYPE_BOOLEAN,  //THE PROBLEM COLUMN
                                G_TYPE_STRING);

GtkTreeModel * sort_model;
sort_model = gtk_tree_model_sort_new_with_model(GTK_TREE_MODEL(store));
gtk_tree_sortable_set_sort_column_id (GTK_TREE_SORTABLE (sort_model),
                ID_COLUMN, GTK_SORT_ASCENDING );
        
tree = gtk_tree_view_new_with_model (GTK_TREE_MODEL (sort_model));      
....
renderer = gtk_cell_renderer_toggle_new ();
column = gtk_tree_view_column_new_with_attributes ("Loaned", 
                                      renderer,"active", 
LOANED_CHECK_COLUMN, NULL);
g_signal_connect_swapped(G_OBJECT(column),"clicked",G_CALLBACK(sort),(int 
*)LOANED_CHECK_COLUMN);

gtk_tree_view_append_column (GTK_TREE_VIEW (tree), column);     
....

then I have the callBack:

static void cell_toggled_callback (GtkCellRendererToggle *cell, gchar * 
path_string, gpointer user_data)
{       
        GtkTreeIter iter;
        GtkTreeModel * sort_model;
        GtkTreeModel * model;
        // tree is static so I get the model out of it..
        model = gtk_tree_view_get_model (tree);
                        
        if(gtk_tree_model_get_iter_from_string(model, &iter, path_string))
        {
                gtk_tree_store_set_value (store, &iter, LOANED_CHECK_COLUMN, TRUE );
        }
}

I get:

(moviecatalog:21175): Gtk-CRITICAL **: file gtktreestore.c: line 912 
(gtk_tree_store_set_value): assertion `VALID_ITER (iter, tree_store)' failed

ANd the toggle is not updated to checked..

Any clues any one ?

TIA,
P_s