gtk_tree_view_column_set_cell_data_func gives GTK-CRITICAL error

[James Steward <jamessteward optusnet com au>]

Hi,

Wanting to display floats with a particular format in a tree view.

void render_float(GtkTreeViewColumn *column,
                GtkCellRenderer   *renderer,
                GtkTreeModel      *model,
                GtkTreeIter       *iter,
                gpointer           user_data)
{
        gfloat  f;
        gchar   buf[20];

        int col = GPOINTER_TO_INT(user_data);

        gtk_tree_model_get(model, iter, col, &f, -1);

        g_snprintf(buf, sizeof(buf), "%.2f", f);

        g_object_set(renderer, "text", buf, NULL);
}

G_MODULE_EXPORT gboolean on_menu_show_results_activate(
                GtkWidget *w,
                GdkEvent *event,
                gpointer user_data)
{

...

renderer = gtk_cell_renderer_text_new ();

col = gtk_tree_view_insert_column_with_attributes (
                GTK_TREE_VIEW (view),
                -1,
                "Title",
                renderer,
                "text", i,
                "strikethrough", j,
                "background", k,
                "background-set", TRUE,
                NULL);

gtk_tree_view_column_set_cell_data_func(
                gtk_tree_view_get_column(GTK_TREE_VIEW(view), col),
                renderer,
                render_float,
                GINT_TO_POINTER(i),
                NULL);
...

}

When I run the app I get:

Gtk-CRITICAL **: gtk_cell_layout_set_cell_data_func: assertion 
`GTK_IS_CELL_LAYOUT (cell_layout)' failed

Can anyone spot what I've done wrong?  There's no compiler warnings, 
just this runtime error.

--
James.