DI API 6.5 and SBO2004: error 100000008 when connecting to db

I am using DI API 6.5 against SBO 2004. In my own environment, the application runs smoothly, but in the customer's environment, DI API gives the error message "100000008" when trying to connect to the company database.

There is one significant difference between these environments: in the customer's environment, the user in question does not have SDK/Add-on licensed mapped to the username. This seems a logical explanation to the problem. But is there some documentation from which I could check out what this error message is all about ?

Best regards,

Henry