Age problem
Greer Garson was only 11 years older than Richard Ney, who played her son. . .and unfortunately (thanks to glamorous lighting, makeup and costuming that only accentuated her relative youthfulness), she looked it. Was impossible--or at least unnecessarily difficult--to believe she was actually the mother of a grown son.
UPDATE: Yes, I am well aware that Hollywood movies are full of instances where actual ages of performers playing mother/son, etc. were chronologically off kilter--but in most cases, there APPEARED to be a big enough age gap that it was convincing. Not the case here, in my estimation--Garson looked like she was maybe 10-15 years older than son tops.