Problem with Server!

HI anyone,

OS of Server system is Linux, and i'm designing a Client&Server
App for my network, and i'm useing from TcpServer,TcpClient,
IdTCPserver,IdTCPclient.
my system in network is called Sysop.
and i use from above components for make a connection between
Stations and Sysop, but only Sysop can send messages(looks like
a simple string) to client.

may linux firewall block client stations to send message or
something else.

Thanks.