I also had the same issue... I filed a bug for this yesterday.
I also tried this: Window->Preferences->Adobe->RDS Configuration.
Error Message: Unable to contact the RDS Server. Connection refused: connect.
Hi,
The RDS connection is refused in the following cases:
1.Server is not running: Check if the server that you have added in the Server manager has its status as running.
2.RDS Username/ Password: While Adding the Server, you need to specify the username and password on the first screen. If this is specified incorrectly RDS connection will fail
3.RDS is not activated: You might have deselected the option during install and so to enable RDS(or to check if its enabled) go to :{CF_Webroot}/WEB-INF/web.xml and check if the RDS section is not commented
This might not be the solution but can you just check if you are successfully able to start and stop server(through console) outside CF Builder and its not throwing any RDS related error on your console.
-Bhakti!
CFBuilder Team