I have not tried to use MySQL yet, I prefer using a flat file system as some of the free hosts I use do not give that ability. But! having said that once you have the database created the form builder creates the table with the name you give it and the fields according to the object names.
I have had problems getting access to databases for other reasons and for me it has been either the host name or user name sometimes the host creates a user name which you have to use.
If you use your file manager to go into the form storage folder I believe their should be a log file that may shed a light on it.
Looks like I will have to set up a form with entry to a database to see what ticks. I do a lot of trials with wamp on my computer so I will knock something up. I have used databases with php so I will have a look and come back.
These are the basic requirements. It is what I use to auto create a database. One of these entries in your case must be wrong.
$dbhostname = "myDomain.com";
This could be Local host or your domain name. Look at the side of your C Panel it should show you the host name. Creating the database in C panel is automatic accessing it is to use their hostname. I think this is your problem.
$dbname = "myDataBaseName";
$dbusername = "myDataBaseUsername";
$dbpassword = "myDataBasePassword";
Open a support ticket with your host and give your settings they will sort it for you.
The Guy from OZ