I don't know if this has been posted anywhere, but I thought I would throw it in here to help people out...
For those of you that have one database user name for both your phpbb2 and dragonfly you can modify the config.php as such to get this script to work.
Note: this assumes that all of your other database information is the same outside of the database name. (e.g. localhost, dbuser, dbpasswd, etc...) But if these were on different servers and/or different user accounts, you would not be reading this 😉
There might be a minor issue in the "db.php": if both your phpbb and cpgnuke databases are owned by the same mysql user, then calling the "mysql_pconnect()" twice with out closing the first connection may cause troubles.
If your converter finishes in 2 seconds, it might the case since every mysql db query returns null value. A simple away to get around it -- grant one of the databases to a different mysql user and put different usernames in the "config.php".