Check out this blog post:
For MS SQL and Azure this would be port 1433, and you would add @servername to your user name in the service configuration such as ‘dreamfactory@r92ul6qcff’.
This forum post also covers the need to format your connection string with username@
. This is documented by Microsoft here.
If this does not help, please reply back with the error(s) from your DreamFactory log.