Help about gr-ieee802-11

hi.i am newbie using gnuradio.when i try run the wifi_loopback is comes
out with this,

Preferences file: /home/userr/.grc
Block paths:
/usr/local/share/gnuradio/grc/blocks
/home/userr/.grc_gnuradio

Loading: “/home/userr/gr-ieee802-11/examples/wifi_loopback.grc”

Done

Showing: “/home/userr/gr-ieee802-11/examples/wifi_loopback.grc”

Generating: “/home/userr/gr-ieee802-11/examples/wifi_loopback.py”

Warning: This flow graph may not have flow control: no audio or RF hardware
blocks found. Add a Misc->Throttle block to your flow graph to avoid CPU
congestion.

Generating: “/home/userr/gr-ieee802-11/examples/wifi_loopback.py”

Warning: This flow graph may not have flow control: no audio or RF hardware
blocks found. Add a Misc->Throttle block to your flow graph to avoid CPU
congestion.

Executing: “/home/userr/gr-ieee802-11/examples/wifi_loopback.py”

linux; GNU C++ version 4.8.2; Boost_105500;
UHD_003.008.002-135-ga393ec83

Using Volk machine: avx_64_mmx
OFDM MAPPER: encoding: 0
set_min_output_buffer on block 10 to 48000
set_min_output_buffer on block 14 to 100000
set_min_output_buffer on block 15 to 10000
set_min_output_buffer on block 17 to 48000
set_min_output_buffer on block 28 to 48000

Done (return code -11)

i also try with this

(gdb) run /PATH_TO_THE_WIFI_LOOPBACK_FILE/wifi_loopback.py
Starting program: /PATH_TO_THE_WIFI_LOOPBACK_FILE/wifi_loopback.py
No executable file specified.
Use the “file” or “exec-file” command.
(gdb) exec-file
No executable file now.
(gdb) file
No executable file now.
No symbol file now.
(gdb) backtrace
No stack.

below is my system info:
user@userr-X455LDB:~$ python -V
Python 2.7.6
user@userr-X455LDB:~$ gnuradio-config-info -v
3.7.7.1
user@userr-X455LDB:~$ uname -a
Linux userr-X455LDB 3.13.0-53-generic #89-Ubuntu SMP Wed May 20 10:34:39
UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
user@userr-X455LDB:~$ gcc --version
gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2
Copyright © 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is
NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.

user@userr-X455LDB:~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=14.04
DISTRIB_CODENAME=trusty
DISTRIB_DESCRIPTION=“Ubuntu 14.04.2 LTS”

what can i do? i hope you can help me.
thanks