I do get a reference of the form like
MyForm = SBO_Application.Forms.Item("MyForm");
MyForm.Items.Item("MyButton").ClickAfter += ...
I also tried directly without reference like
SBO_Application.Forms.Item("MyForm").Items.Item("MyButton").ClickAfter +=
No luck !
This has already worked in the past so I don't know the small thing that makes it not working