The "X" on the GE form usually means one of two things:
1) The facial recognition program doesn't register because is not looking at the camera lens when first inserting his passport.

2) His fingerprints are not scanning properly. This is the most common reason for getting an "X". He is probably separating his fingers when placing them on the scanner. Tell him to try it with the sides of all 4 fingers touching. This use to happen to my spouse often until an Immigration Agent taught her the proper way to scan her fingerprints.