server closes client connection right away

Hello,
I'm writing an echo server /client application using C++, and I have
this problem, the program runs fine under my linux box, its FC4, but I
sent it to some guy to test it and he tells me that as soon as a
client connects it disconnects,
for example
../echosrv
Client 0 connected from 127.0.0.1 and port 43402
Connection closed for client 0
Client 1 connected from xx.xx.xx.xx and port 35272
Connection closed for client 1
and this happens if you try to connect from a localhost or from a
remote one,

does anyone has any idea, why this could be happening,

regards, Yazan