Thx for your quick answer! You realy helped me to solve my problem.

The problem was indeed the secound "NULL" in my Button define.
I have schwitched this:
button = (0,0,pcx_btn_resume,NULL,NULL,NULL,NULL,NULL);
to this:
button = (0,0,pcx_btn_resume,pcx_btn_resume,NULL,NULL,NULL,NULL);
and now the button is visible.