Assetbundle problem: it was not built with the right version

Hi ....

I'm trying to use assetbundle in Unity 5.5 , but I always get this error message .

"can't be loaded because it was not built with the right version or build target"

I use this code to create the assetbundle

 BuildPipeline.BuildAssetBundles("Assets/AssetBundles/CreatedBundles/Android", BuildAssetBundleOptions.None, BuildTarget.Android);

In android device, I use this code for downloading and importing the object that called "MODEL" from the assetbundle.

 void Start()
 {
      StartCoroutine(DownloadAndCache(URL));
 }
 
 IEnumerator DownloadAndCache (string Path)
 {
        using (WWW www = WWW.LoadFromCacheOrDownload(Path, 0))
        {
            yield return www;
            AssetBundle loadedAssetBundle = www.assetBundle;
 
            //AssetBundleRequest request = loadedAssetBundle.LoadAssetAsync(ObjectNameToLoad, typeof(GameObject));
            //GameObject gameObject = Instantiate(request.asset) as GameObject;
 
            GameObject gameObject = GameObject.Instantiate(loadedAssetBundle.LoadAsset(ObjectNameToLoad) as GameObject);
 
            Model = gameObject.transform;
            Model.parent = transform;
            Model.position = new Vector3(0, -2.0f, 0);
            Model.localScale = new Vector3(2.5f, 2.5f, 2.5f);
            Model.localEulerAngles = new Vector3(0, 180, 0);
 
            loadedAssetBundle.Unload(false);
        }
 }

Where's the problem ?

Notes :

• in Editor working fine

• in old versions of unity, this code was working fine.

Thank you ...