Greetings Sir,
I'm specialized in looking for bugs in flash applications and I think I can solve this for you. I have more than 5 years of intensive working in flash and related platforms from which I have got a decent experience knowing why a flash application may stop to work. Said that, I will be happy to support you and solve your bug.
Regarding the application you said that you only got the air and the post installation files from your developer. Don't you have also a bunch of *.as files (actionscript files) or a *.fla or *.mxml? In order to solve the problem we will need to compile the application from its sources, if you don't have the sources there is not much we can do to be honest. I will be looking forward to hear from you.
Sincerely yours,
Robert