There are several possible reasons why the approval from your email notification does not work:
If you click on the Approve button and see a window with the message "Updated", it means that the request was updated after the notification had been sent. If this is the case, please close the notification window, refresh the browser window, check the updated request, and then make a decision.
If there is an error message saying the document cannot be found, it means that either the document was deleted or you've been removed from the list of Approvers.
If you are not able to click on the buttons, there could be a problem with your email client. It is a typical issue in MS Outlook that the "Reject" or "Approve" buttons do not work. The solution to this problem is described in the Microsoft support article Hyperlinks are not working in Outlook .
Please contact us, if the problem persists.