Loading Asset bundles on iOS device

Hello,
I have a problem loading asset bundles from local server or Amazon CDN on Ipad and Iphone, it always return me an error :

The AssetBundle ‘bundleName’ could not be loaded because it is not compatible with this newer version of unity runtime. Rebuild the AssetBundle to fix this error.

I am using Unity 5.6.1p4 , and AssetBundles are loading perfectly in editor, standalone build and Android devices. I am sure asset bundles are built for iOS platform , I am loading bundles using WWW.LoadFromCacheOrDownload ,and asset bundle version is set higher than previous one.

This problem is bugging me for couple of days, and I just cant find the solution, neither anything similar here.

Anyone had this problem before?

Thanks

Reply to myself,
I’ve finally succeded in loading bundles on device. The thing was scripting backend was set on Mono2x , and for iOS arm should be set to IL2CPP.