Sometimes Dentrix installs require a Dentrix Passphrase, and other times a User ID and Passphrase, what is the difference?
The 2 windows that you are seeing above are based on the office's preferences.
If they have Passwords turned on in Dentrix, then you will get the login prompt for a Dentrix Administrator's username and password (Picture #2).
On versions G6.2+ they will have to create a database passphrase no matter what, so if the office does not turn passwords on it will default to prompt them to enter their database passphrase for access to the database (Picture #1)