[Discuss-gnuradio] connection fails, No UHD Devices Found

It is very annoying that sometimes I can not connect to the device using this command:

~$ sudo ifconfig eth0 192.168.10.1

I can ping 192.168.10.1, but ping 192.168.10.2 fails:

~$ sudo ifconfig eth0 192.168.10.1
~$ ping 192.168.10.2
PING 192.168.10.2 (192.168.10.2) 56(84) bytes of data.
From 192.168.10.1 icmp_seq=1 Destination Host Unreachable
From 192.168.10.1 icmp_seq=2 Destination Host Unreachable
From 192.168.10.1 icmp_seq=3 Destination Host Unreachable

~$ uhd_find_devices
linux; GNU C++ version 4.7.3; Boost_104900; UHD_003.006.000-0-g7788c692

No UHD Devices Found

-----------------------------------------------------------------------
Ubuntu 13.04, gnuradio 3.7, usrp N200
-----------------------------------------------------------------------

Why does it happen?
How can I connect to USRP device?

Thanks in advance!
--
NE