No Automatic Alias box when editing a node?

Hi All,

I seem to have abit of a problem.. when I goto to edit a node usually there is a checkbox for automatically aliasing or setting my own... currently all I have is the bleow, would anybody know why this is happening?

"Optionally specify an alternative URL by which this node can be accessed. For example, type "about" when writing an about page. Use a relative path and don't add a trailing slash or the URL alias won't work."

Tks.