Thanks Simeon Bateman!
For all those who also trying to migrate for the Flashbuilder 4.5 here is the reference based on my experienced.
After I did all these following steps it is working fine:
*Changed Adobe AIR version 2.5 into 2.6 in the myGame-app.xml
*Flash builder4.5 > Project > Properties >ActionScript Compiler>Use default SDK(currently"Flex 4.5")
*Flash builder4.5 > Window > Installed Flex SDKs>Flex4.5
*Flash builder4.5 > Project > Properties >ActionScript Build Path>Remove flex hero> Add Flex SDK >Flex 4.5