Thanks for your answer..
Well ,untill now i didn't know what was jumbo frame, and no i didn't enable it ,well i beleive that i have to enable in my router or in my lan card,isn't it?
Also ,i read the link viewtopic.php?f=6&t=11555
(how to send the kernel log) ,and now i have the debug.dat file.
But ,where i have to send it? i look for a email from a synology assistant but i can't find it.
Thanks again for your help