This is likely caused by one of the below options.

1. You have the wrong public IP address on the client.
   
   On the ThruLink client, as part of the Encryption Tunnel configuraiton you are required to input the name and public IP or DNS address of the server location.  If this IP is not the correct IP address then the client will never get a connection to the server.
   
   The public IP address should be the IP address the network provider at the server side location provides.  If this is not a static public IP address then it will change, in which case ThruLink may connect and then disconnect and not connect again, so you need to consider using a dynamic DNS address such as No-IP or Dyndns on your server side router.
   
   
2. You have incorrectly configured the Encryption Tunnel page on the client
   
   There re several key requirements on the client in order for it to be able to establish a conection.  The Pre-shared key on all clients should be the same as the server, The server unique hostname should also be present on each client and of course the public IP address of the server needs to be in the encryption tunnel configuraiton.  You also need to ensure all ThruLink devices are using the same port and are all equally set to either Route mode or Bridge mode.
   
   If one or more clients have a mis-configuration in the encryption tunnel page then they will not connect.  Note it is also possible to mistakenly cnfigure 2 or more clients with the same LAN IP address which can also cause connection related issues.
   
   We advise, if you have more than 2 clients to connect to a single server, configure one client, confirm it is working and links up correctly then download the configuration from within the GUI.  On the new unit, simply upload this configurartion, and once the unit has restarted, login and change the unique hostname and LAN IP address of this unit.  The remaining connection details should work since they have been tested already.