As a Site Factory user, you are unable to log in because your user account does not exist or is blocked.
My account does not exist.
Users are added manually to your Production Factory when your site is provisioned or from Factory administrators.
The way that users get added to the non-production Factory is through a staging process in which you restage from your production factory to your non-production factory.
My account is blocked.
Users are blocked on any Factory dashboard after 30 days of inactivity. Please contact Acquia Support who can re-enable your user account on your production Factory. You can then restage from production to your non-production factory using the documentation provided previously.