I think you are talking about a Test-Drive. When you launch a Denodo Test Drive, the Denodo web site shows you an option for downloading a RDP file just after a few minutes. You will also receive and email with similar information. If you open that RDP file and you select the correct password then you should be able to connect to the Test Drive.
If you are having issue with RDP, please check the configuration of your system as you could have internal restrictions in your system and you are not allowed to use RDP.
I have done a test right now and I was able to connect to my RDP without any issues.
Please keep in mind that Test Drives has a duration of 2 hours, so maybe the time has expired for you. If that is the case, you could launch another Test Drive from the website, and in this case you could explore a different one.
Hope this helps!