Exporting a project for player 10 to player 11 (or AIR 3.x), if you are using JSON, a compile error is triggered. This is because on player 11 there is an internal, faster JSON parser. Use JsonMan class to transparently compile for both players without errors.
This morning I have started working again on a large project I am due to deliver in 10 days, and to my surprise, as soon as I opened the fla file, I got screwed by Flash, and had this output: "Flash can not parse this document."
In this post I explain how I managed to fix the corrupt file and get it to work again.