Critical Errors on some functions

[ghost]

I've got this message

(gvirc:5446): Gtk-CRITICAL **: IA__gtk_widget_set_size_request: assertion 'GTK_IS_WIDGET (widget)' failed

when I tried to do

var x,y int
MainWindow.GetSizeRequest(&x,&y) //Window object
ConnView.SetSizeRequest(x/4,y) //TreeView object

and this kind of message

(gvirc:15681): Gtk-CRITICAL **: IA__gtk_notebook_insert_page: assertion 'GTK_IS_NOTEBOOK (notebook)' failed
panic: runtime error: index out of range

and crash when I tried to do

ConnList.InsertPage(someBox,someLabel,0)

or

ConnList.AppendPage(someBox,someLabel)

Is this bug in go-gtk or not? P.S. Sorry for my bad English

[mattn]

Could you please show me whole of your code?