Custom formula issue

Hi experts,

I've created custom formuls as in the following document:

http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/503fb957-4f9b-2e10-4a8a-fa7c604ae37d?overridelayout=true

But i can't see them. I don't even have the choice User defined functions (I respected all the steps and the most important activation).

Does someone faced the issue before?

Thanks.

Amine