reason of unloding application instance?

I am creating a small chat application using Flash Media server. I have already created all my user interface components in Flex(Adobe AIR).

problem what i am facing is this when i am sending Object through Flash Media Server, some objects send successfully but for some objects it become a problem and Flash Media Server unload application instance.

     So i would like to know the reason of this problem, and how to get rid of it?

please help me.