Large data transfer Failed!!

We got a very serious problem..

Our VOD box has a connection with cable modem..
During service, we recognized there is a disconnection
between modem and Main board, specially in large data
transfer..
But, In XP(not XPE), we could not find the problem..
We added almost QoS component like RSVP,,
We tested our H/W.. and no problem..

Is there anyone to experience our problem? Is there some
component we should add?

I hope I get any answer~!!!