[Discuss-gnuradio] Awgn simulation error

Hi,
I had run the sim.grc in the awgn simulation folder from gr-ieee802.11 and I get this following from the terminal. Plus, I'm not sure how I should measures the ber however the error I got is below. Thanks
linux; GNU C++ version 5.4.0 20160609; Boost_105800; UHD_003.010.001.HEAD-0-g929e3b32

MAPPER: encoding: 0
set_min_output_buffer on block 9 to 397056
set_min_output_buffer on block 11 to 397056
set_min_output_buffer on block 13 to 397056
set_min_output_buffer on block 14 to 397056
set_min_output_buffer on block 16 to 397056
set_min_output_buffer on block 28 to 96000
thread[thread-per-block[1]: <block random_periodic_msg_source (27)>]: pmt_to_long: wrong_type : #t