After a a few hours of grinding out the last bits of functionality, I went to build my AIR file and was greeted with a very unhelpful message:

Error creating AIR file
Usage error (incorrect arguments)

Eh? Debugging showed no errors, and I'm running strict. I turned up NOTHING on this error in documentation or searching. But I remember that I've been hand editing the app.xml (aka application descriptor) file for the project and figured I mucked something up in TextMate. 

I removed the old file, recreated the settings in Flash > Commands >  AIR - Application & Installer Settings, and then built the file. Viola! No errors.

So, I decided to compare files. Remember, the error says "incorrect arguments". Um, no. Far as I can tell there's an encoding or white space issue going on. 

Modifying settings in Flash and resaving does NOT fix any formatting issues. It's saves fine, but you'll still get errors. 

I copied over my size settings, and saved the file. This time I get a nice new error:

Error creating AIR file
Unexpected or unknown element or attribute in the application descriptor file.

At least this time Flash points me to the write file. In short, if you start getting errors building your AIR file like this, look to your "application descriptor file" and be careful...it's fragile.

If I didn't think someone else already had the motto, I'd coin "I break it so you don't have to".