didn't west ham do soething similar about 5 years ago, and had to replay the tie???
They brought on a sub for the last 5 minutes of the game which they were winning at the time against Villa. The bloke who came on had played for a non-league side in one of the qualifying rounds I think. Even though it was only 5 minutes, they were made to replay the tie, which of course they ended up loosing, and therefore went out.
Same thing though really, they both played players who were ineligible to play. Its just the FA have one rule for the 'big' teams, and one for the others.