Class is not initialized

Dear all,

I am a newbie in the Allegro CL programming. I can't
figure out how to solve this pogram error I got. 
I create a class that is a subclass of the dialog
class, and set the class property of a form to that
class. I put some widgets in that form such as single
item list and static text. My definition of the class
is like this:
 (defclass my-class (dialog)
   (open-another-window 
    :accessor open-the-window
    :initform nil))
I use the accessor slot to open another (pop-up)
window.
My problem is, I will get this error message:

Error: Class #<STANDARD-CLASS MY-CLASS> is not yet
finalized.
[condition type: PROGRAM-ERROR]

first time I open my project and do something at the
form (even only maximizing that form from its
minimized state). However, I am not getting this error
message whenever I run the project first and then do
something at the form.
Could anybody please help me to solve this problem,
what is I have done wrong?

Regards,

Opim S Sitompul
PhD Student
National University of Malaysia


__________________________________
Do you Yahoo!?
The New Yahoo! Search - Faster. Easier. Bingo.
http://search.yahoo.com