SW1,
I've certainly heard of people failing flight grading before. There was someone on my FG who was sent home before the sims because he wasn't performing. This isn't to say you weren't hard done by, but perhaps they are holding a pretty high standard for advanced entry. I know the advanced entry guys and girls who got through were averaging 4.5 out of 5 the whole time. My advice would be to email Cathay, and make your self available for the ab initio course. Its only an extra 8 months, and the standards at flight grading will be lower
RL