Kind of an interesting phenom for me here. I've been working with Jan 6 Nightly build and making progress on the Windows side. I'm using the nightly build plus AIR 2.0 beta and the AIR 2 beta runtime.
On the Mac, I get one display of the app and the next time I get a message saying that the SDK (nightly 4). Think it might be a bad build as there are only 2 files in the bin folder.
OK, so it's some interaction with the Beta AIR runtime. I've gone back to 1.5.3 and it seems to be working OK now.
If you are experimenting with Air 2 or flashplayer 10.1 ,you are better off establishing a new workspace and go through all the steps to have the sdk updated and adjusted to suit that environment.
Also the fp 10.1 beta debug plugins are now available which makes it much better in flex when playing with 10.1