Hi Danilo,
If you've set the UseTrusted property to true then the database connection will be using Windows Authentication. This means that whatever Windows account your web service is running under needs to be set up with permissions on the SQL Server (minimum recommended by SAP is db_owner privileges on the SBO-COMMON and company databases if using the DI API).
Alternatively, you can set UseTrusted to false and then use the DBUser and DBPassword properties to set a specific SQL user for the connection. Again, this user needs to have db_owner privileges on those databases.
Kind Regards,
Owen