Which of these steps did they fail to include?
http://www.zen-cart.com/content.php?...fferent-server

Zen Cart's database connection is simple:
1. reads the DB_XXXXXX values from configure.php
2. PHP tells MySQL to connect using those credentials
If you get an error, then the credentials are wrong (or haven't been created in MySQL, which still of course makes your credentials wrong).

Caveat: If you use a different DB_PREFIX between servers (this matter is mentioned in the above FAQ article), then your database tables won't be found. But that won't cause a "can't connect to database" error; it would say something like "table doesn't exist", which is a different issue than what you describe.