Hello, i am a newbie and i a just install osmo tetra under ubuntu 11.10

When i go :

cd osmo-tetra
cd src
cd demod
cd python

and launch

python tetra-demod.py

This is the terminal answer

gr_fir_ccc: using 3DNow!Ext
sample rate: 195312
in.dat: No such file or directory
Traceback (most recent call last):
  File "tetra-demod.py", line 67, in <module>
    my_top_block().run()
  File "tetra-demod.py", line 45, in __init__
    IN = gr.file_source(gr.sizeof_gr_complex, options.input_file)
  File "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/gnuradio_core_io.py", line 385, in file_source
    return _gnuradio_core_io.file_source(*args, **kwargs)
RuntimeError: can't open file

What is the problem ? i can't continue with this files problems.

Thank for your help.