Questions about benchmark tx/benchmark rx with USRP N200 & GNU 3.7

Dear All,

I am trying to transmit something and receive it back using the second
USRP N200 device.
However it fails, or I did not do it correctly.

I have two laptops and two (USRP N200, XCRV2450 db, 2 vert2450 antennas
for each)s.
GNURADIO v3.7 is installed to Ubuntu 13.04.

I run in the first laptop this command:

sudo ./benchmark_tx.py -f 2.45G -A J1 --spec A:0

In the second one I run this:

sudo ./benchmark_rx.py -f 2.45G -A J1 --spec A:0 --snr 10

But gives me:
TIMEOUT
TIMEOUT

I changed the sampling rates also did not work.
I played with the frequency also did not work.

What can cause this?
Is this a hardware problem?