It seems that you don't have lablgtk2 installed.
Please check whether $(OCAMLLIB)/lablgtk2 exists or not.

N.P.S.Sika@westminster.ac.uk wrote:

>Hello there,
>
>I try to compile my first GTK+2 code "base.ml" taken from the GTK Ocaml tutorial
>from
>
>-------------
>(* file: base.ml *)
>
>let main () =
>  let window = GWindow.window () in
>  window#show ();
>  GMain.Main.main ()
>
>let _ = main ()
>-------------------
>You can compile the above program with ocamlc using:
>
>ocamlc -I +lablgtk2 -o base lablgtk.cma gtkInit.cmo base.ml
>
>
>HOWEVER when I do that i get the following error message
>
>File "base.ml", line 4, characters 15-29:
>Unbound value GWindow.window
>
>anyone got any idea what it is ?
>thanks
>
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>  
>