Error deleting widgets: assertion `GTK_IS_WIDGET (widget)' failed

[Jacob Kolding <jacob omnia dk>]

Hello all

I have some problems deleting widgets. In this case:
GtkCellRenderer
GtkTreeViewColumn
GtkTreeModel
GtkTreeSelection

The code looks like this:

gtk_widget_destroy((GtkWidget*)check_renderer);

and the error I get:

Gtk-CRITICAL **: file gtkwidget.c: line 1626 (gtk_widget_destroy):
assertion `GTK_IS_WIDGET (widget)' failed

Can anyone tell me what I'm doing wrong?

Thanks in advance.

/Jacob Kolding