It depends on the school. It could be a physical profile, a lapse in security clearance, failure to be qualified in MOS, lack of time left to meet SRR. You need to provide more details.
You sure are concerned about your "friend's" situation. Let him handle it. Maybe if he did not have an issue with his ex-girlfriend, he would have not lost his shot at DS school. Live the Army values and things should be fine. It is that simple.