Help with a script to get an object to rotate slowly without your player moving

Hi Guys, My problem is with this script.

var turnSpeed = 5.0;

function Update () { transform.Rotate((Input.GetAxis("Vertical") * turnSpeed) ); }

I've just spent about half an hour moving characters around because they were 'expected' at certain points. Now after everything is where it is expected to be, I get this error.

Assets/Scripts/Rotate.js(4,21): BCE0023: No appropriate version of 'UnityEngine.Transform.Rotate' for the argument list '(float)' was found.

Help please, it's for my school project that needs to be handed in in 4 hours. Thanks in advance :D