I haven't seen this error personally, but it might be worth comparing
it to the most recent app they made.
At the most recent meeting, the created an Air app, and if I remember
correctly that app used 4 different icon images. So maybe start by
comparing what you have to this..
http://svn.adogo.us/200808/LuncChooserAppAir/
Also, I seem to remember in the meeting, that you could only use PNG
files, so maybe that has something to do with your error.
Hope this helps,
Daniel