switch connected to the linux board hangs up

i use embedded linux.
switch hungs up after transmitting data from board (uClinux 2.14.19 kernel, realtek 8201 PHY) to PC using ftp.
i have to off and on switch to make it functional again.
is any body knew something about this problem?
thank you.

Welcome to LQ!

I've had this problem when playing with an embended system with uclinux 2.4.
I had a 3com switch which sometimes stopped working. I did look for the problem, I tried with an other switch (the exact same model, but a different part number, newer) and the problem disappeared. It was the only problematic switch out of 10. Maybe you're PHY is loosing link or a duplex problem?? Electrical problem??? I did not dig into the problem as changing the switch solved it.
Still this problematic switch seemed to work well with PC.

So I can just tell you that it happened to me... maybe borrow someone else's switch or hub.

Thank you for answer.
well. it is something like methaphisycal problem. My switch works with PC great.
Therefore packets from embedded system is worster than from PC. I can't understand it.
I need to ensure that it is hardware problem.
if it is not - that is my (programmer) problem.
(it is very bad practice to remove own problems to someone else)
I still asking for help.