problems with placing dynamic stamps over javascript

I can place a stamp with:

this.addAnnot({page: this.pageNum, type:"Stamp", AP:"Draft", rect:[144,72,144,72]});

all works fine, but if I change the static stamp to a dynamic stamp (for example Approved with name and date) I will only get a black rectangle with a cross inside.

I have checked the stamp name to choose the correct one. As I said before with static stamps no problem.

I'm using Acrobat XI Version 11.0.11

Any hints what's going wrong?

Thomas