Windows 2008 R2 with Hyper-V losing network connection

i have windows 2008 r2 enterprise server hyperv. created virtual machine running windows 2008 r2 standard.
i have second physical computer running windows 2008 enterprise, opened 2 command prompts; from one command prompts run ping -t <win2008 r2 host> , other 1 run ping -t <win2008 r2 vm>. 2 ping expected responses in less 1 ms

from win2008 r2 vm run wbadmin start systemstatebackup -backuptarget:\\<win2008 server>\share\

pretty after backup starts, pings start failing: while there successful responses (some of them after quite long time, 1500 ms), of returns either request timed out or destination unreachable !
on vm, wbadmin was able find files (~72k) , repeatedly displays found <72k> files (the same number).
i see vhd files on target growing pings did not improve @ all. backup failed after 1 , half hour.

i have disabled tcp chimney , rss on 3 oses hoping fixes problem not.

it seems problem caused virtual adapter created hyper-v .
i removed adapter (from hyper-v network management), stopped hyper-v , ran wbadmin backup host's system state same network share (as in original test, vm) , looks network connection between 2 computers stable; did not not 1 request timed out.

the computers clean (installed short time ago) no other software installed. have 2 nics 1 of them configured , connected network.

has had similar problems?

thanks,
dan

i have.

unfortunately have not find solution yet. reason posted establish problem not random, isolated incident.

Windows Server  >  Hyper-V