There are a couple of conditions that must be met:
  1. The email campaign must be configured to allow for autologins
  2. The link to the User Profile page must be correct.
  3. The site must be configured correctly on the backend by support.
If you have verified the first two items, contact support to verify the third.

Note: Autologins are only valid the first time the link is clicked. Additionally, there is a site setting than controls how autologin functions when the email message is forwarded. By default, this option is turned off to not allow forwarded emails to have autologin links that function.