The Unknown host specified error usually occurs if the host in which you have the Denodo Platform 8.0 is running is not able to reach the host where you have the Data Source.
In such situations, I would try to **ping** the host from the server where you have the Denodo Platform to see if the host is reachable. Also, you can check if there is any firewall which was blocking the connection to this server.
You can also review the **vdp.log** file under the "<DENODO_HOME>\logs\vdp" directory for more information on the error occurence.
Hope this helps!