How can i convert Assetbundles build in 3.5 work in 4.2?

I have a lot of Assetbundles build in 3.5,but unity3d 4.2 don’t support older version builded Assetbundle,they can’t work in 4.2

is there any way can I decompress old Assetbundles(because i don’t have the assetbundle’s source file),and rebuild them in 4.2 version?

who can give a advice?

thanks a lot and a lot!

You can open the assetbundle and extract all assets with an install of Unity 3.5 (using AssetBundle.LoadAll() and some AssetDatabase functions to save all your assets to your project)
But if you are not in the original project of this asset bundle, you will not be able to recover shaders and scripts from the assetbundle because they are only stored in the compiled project and not in the asset bundle.

Then, if you achieve this step successfully, move the assets to Unity 4.2 and re-compile all the stuff…

Anyway, I don’t think there is an easy way to do this if you don’t have your original 3.5 project and assetbundle sources…