Currently you will be to connect to one client system using Gateway Server.
Note: - Release 5 Multi user you can open multiple instances of Tally and there is no such restrictions.
To connect client system via Gateway server, open Tally folder (Tally.ERP Rel 4.93) > Open tally.ini file > mention Gateway Server name and Port number, save the file and reload Tally.
Or open Tally. Click on reconfigure existing license > Single user > Select existing Multi user > mention Gateway Server name and port number. Accept and restart Tally.
Note: - In case if you try to load one more instance of Tally then Tally will throw error message as shown below.