dereferencing

["Mustafa Sanver" <msanver hotmail com>]

Hi,
Any idea how to solve this dereferencing problem? Thank you in advanced.

========= ERROR ========
GtkNotebookPagegtsrc.c: In function `set_notebook_tab':
gtsrc.c:144: error: dereferencing pointer to incomplete type

====CODE ========
/* This is an internally used function to set notebook tab widgets. */
void
set_notebook_tab    (GtkWidget       *notebook,  gint             page_num,
GtkWidget       *widget)
{
  GtkNotebookPage *page;
  GtkWidget *notebook_page;
  page = (GtkNotebookPage*) g_list_nth (GTK_NOTEBOOK (notebook)->children,
page_num)->data;
  notebook_page = page->child;  // LINE 144
  gtk_widget_ref (notebook_page);
  gtk_notebook_remove_page (GTK_NOTEBOOK (notebook), page_num);
  gtk_notebook_insert_page (GTK_NOTEBOOK (notebook), notebook_page,
                            widget, page_num);
  gtk_widget_unref (notebook_page);
}