Unable to open connection to hypervisor URI 'qemu+ssh://root@IP:port/system':
cannot recv data: Host key verification failed.

: Connection reset by peer
Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/connection.py", line 971, in _try_open
    None], flags)
  File "/usr/lib/python2.6/dist-packages/libvirt.py", line 111, in openAuth
    if ret is None:raise libvirtError('virConnectOpenAuth() failed')
libvirtError: cannot recv data: Host key verification failed.

: Connection reset by peer

Maybe you need to install ssh-askpass in order to authenticate.