CurrPage.EDITABLE(FALSE);

I have this code in an Action button of a New page I've created.

The idea is that if I call my "post" function, and it returns "TRUE", the page should not be editable at all

Register Receipt - OnAction()
IF (MyCodeUnit.Post(Rec)) THEN 
   CurrPage.EDITABLE(FALSE);

However, this is not working. The page is still editable, even after "CurrPage.EDITABLE(FALSE);"

Any ideas on why it's not working or how to achieve this behaviour??