I just got off the phone with Netflix support. Specifically for Iron Man 2 and one of the Transformers movies it's a known issue. There is a temporary fix:
1. Sign in to netflix.ca
2. Change your account settings for video quality to anything except Best/HD.
And that's it. I just tested it myself and it worked. He said you may have to wait an hour for the changes to come into effect, but I just logged out and then logged in to my Apple TV Netflix and it was done.
He also mentioned this is a temporary workaround and they are working on it. Basically when they rent movies for use, they are given a package of different qualities and languages and they accidentally put the French HD in the English HD "slot".
Hope that helps!
EDIT: This solution is only in direct response to X1Zero's problem. Sorry, OP.