Port Server TS4 client connect problem

I have buy the Port Server TS4 to replace our old Modem Server.Coz all client will upgrade to win2k .
But there has some trouble ,sometimes client’s computer will disconnect the Port Server(I can ping and telnet the port server) or sometimes connected but after reboot the computer it will lost the connection too.But all has Digi com port in Win 2k “System Manager”.What happen ?
It’s there has client connection limit in port server TS4,coz there has 20 client’s connection it .

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