Hello,
Infopath does not have built-in functionality for you to submit to the DB from a secondary datasource. But you can do it if your Main datasource is a dataconnection to the DB. There are a few times when submit is not allowed in the Main datasource also and the reasons for this are mentioned in the last screen of that data connection.
One other way of submitting is to do it entirely in c# code using SQL Client connections. One important thing is that to submit to a Database a form needs to have full trust otherwise you cannot submit to a DB.
Hope this information helps!
Shanthi
InfoPathDev India
Shanthi Reddy