This message indicates that a network problems occurred, please check the following :

1- Check out the IP address of the server you are trying to access. The IP address (private or public) set on your client must match the IP address of your server. It is advisable to have a fixed IP address set on the server to avoid the automatic change of the address that can occur when using DHCP. If you are trying to connect from a remote location using the public IP address, make sure that you have subscribed a fixed public address otherwise changes can occur,  contact your Internet service provider for more information on this feature. It is also possible to use DynDns services to avoid this trouble.

2- Check your firewall settings. By default, inbound and outbound connections on TCP port 3389 must be enabled. Firewall can be located in various places such as your Internet connection router, or also your windows firewall, or firewall/antivirus software.

3- If you are trying to connect from a remote location, a redirection (or port forwarding) rule must be activated on your router.

4- Antivirus software can sometime block TSPlus. To avoid this, place an exclusion rule on the following folder :

                 - C:\Program Files (x86)\TSPlus

                 - C:\wsession

5 - With the AdminTool, verify the status of your TSplus license.It is important to know if your issue is related to a TSplus license or to a Windows system problem.
If your current TSplus license is invalid you will need to install the latest TSplus update and activate a new valid one.

Open a windows explorer and locate the license.lic file in the following path C:\Program Files (x86)\TSplus\UserDesktop\files and apply your license again.

Then reboot the server,

6 - In case of incompatible Updates that has been installed on your system, the solution is to download and run the latest update on your server :

For old releases (5.xx and below) the TSplus technology cannot match with the latest versions of Windows, so you will also need to update.