what is the use of anti-forgery token salt?

In ASP.NET MVC 1.0, there is a new feature for handling cross site request forgery security problem:

 <%= Html.AntiForgeryToken() %>
[ValidateAntiForgeryToken]
public ViewResult SubmitUpdate()
{
    // ... etc
}

I found the token generated in html form keep changing every time a new form is rendered.

I want to know how these token is generated? And when use some software to scan this site, it will report another security problem: Session fixed. Why? Since the token keep changed, how can this problem come ?

And there is another function, that is "salt" for the antiForgeryToken, but I really know what this used for, even through we don't use "salt" to generate the token, the token will changes all the time, so why have such function?