In this case, I would suggest you to check the following.
1. Make sure the version of the Virtual Dataport Administration tool is same as the Virtual Dataport Server that you are trying to connect with.
1. If the Virtual Dataport Administration Tool and Virtual DataPort Server is running on the same machine. then try connecting using the server URL //localhost:9999/admin
1. if the Virtual Dataport Administration Tool and Virtual DataPort Server is running on the different machine, then make sure the (RMI host name or ip address) and port is accessible to the client machine that connect to the Virtual Dataport Server.To know more about the RMI hostname, refer to [Set the Hostname of Virtual DataPort Server](https://community.denodo.com/docs/html/browse/latest/platform/installation/postinstallation_tasks/change_the_host_name/change_the_host_name#set-the-host-name-of-virtual-dataport) section of the Denodo Platform Installation Guide.
1. if the default password are not changed, then try using admin/admin to connect to the Virtual Dataport Server.
1. Analyse VDP.log and VDP-Admin.log for more information.
For more information, refer to the [Denodo Platform for AWS 7.0 Quick start Guide](https://community.denodo.com/docs/html/document/7.0/Denodo%20Platform%20for%20AWS%207.0%20Quick%20Start%20Guide).
Hope this helps!