what do I do wrong?

[Paul Argentoff <paul@paul.rtelekom.ru>]

Hi all!

Recently I've started to learn MzScheme, because found this GUI scheme 
implementation useful for my research project. Surely, I've read some of 
GUI Application Framework manual and other MzScheme docs. So I don't 
understand why the following code:

;; libs
(require-library "framework.ss" "framework")

;; code

(define frame (make-object frame:basic-mixin% "label" #f 500 400))
(send frame show #t)

... produces this error:

7.28-7.46: reference to undefined identifier: frame:basic-mixin%

???

I think I'm doing something wrong. But what?

BTW, I use DrScheme 1.0.3.