build a flash .

As the title .i've got troubles on building a flash.
unity version : 3.5.1
file to be built :Angrtbots (the peoject povided by unity)

what did I do:
1.open file : Angrybots.unity
2.click file - build settings
3.choose Flash player
4.click swith platform
5.click build and run

and then ,the file was opened with IE. but I got a black sreen only ,with words "developmen build"

Why? Where is my fault?

help me plz.