Why does my asset bundle can't load by iOS4.3.3?

such as title,I was build a iOS type asset bundle file by unity4.2, It’s running good at Editor and iOS6.0 device
but,when I load it in iOS4.3.3 device, It’s crashed!

In your player settings there is a setting for building for a minimum version of iOS. Could it be your player is being built for 6.0 devices and better? I think asset bundles inherit some aspects of the player settings.