I'm sorry if this is not helpful and is just my own confusion, but here it is:

Earlier in this thread you were calling the user "sapsidadm". Later, you were hiding part of the name, XXXXadm. Then you gave "getent passwd" output. Within that output, there is no "sapsidadm". So I'm not sure how to check the validity of your user entry. But *if* the real entry is "sapadm" then I note that it is using shell /bin/false. This could explain why you can't su to that user.