Forcing a customer to log in/register at checkout

To allow only logged in customers to check out:

1. Log in your administrator panel and click on the Settings link in the ADMINISTRATION side box.
2. Select the Disable anonymous checkout check box and click on the Update button.
   

   NOTE: After that the unlogged customer will not be able to check out without registering, he will need to fill in the User account info section on the Customer information page.