iTween - Unknown identifier problem

I'm a newb to using Unity and have discovered the iTween tool. I have created a Plugins folder and have placed the script in there. But when I attempt to follow the basic tutorial, that tweens the block up , Unity gives me error messages saying there is an unknown identifier

Assets/Standard Assets/Scripts/Tester.js(3,9): BCE0005: Unknown identifier: 'iTween'.

The code is the basic one supplied.

function Start () { iTween.moveTo(gameObject,{"y":2}); }

What am I doing wrong?

For ref Im using a Mac and iTween 2 and the most up to date version of Unity