Object is not loaded from the server

Hi,

I have generated the prefab in unity and i uploaded it to my dropbox. I put the name as Cube.unity3d. And i have added this script in one of my empty game object.

function Start () {
	var www = WWW ("https://www.dropbox.com/s/drvaucv7l61c77g/Cube.unity3d");
	yield www;
	// Get the designated main asset and instantiate it.
	Instantiate(www.assetBundle.mainAsset);
}

When i play the unity editor the that asset is not coming rather it is showing the error.

Please help to solve this issue. I am using unity4.3.1.

Here is that dropbox link:
https://www.dropbox.com/s/drvaucv7l61c77g/Cube.unity3d

Thanks.

In unity4.3.1 i cannot able see this asset bundle option.
1587528--95071--$Capture.PNG

what should i do to get this?

This is the first time i started working on assetbundle.

please help me to do this.

Thanks.

I only assume you know that assetbundles are for Unity Pro, right?

Yes i knew, i am using unity pro only.

any update?