Audio source - device or resource busy error

[Elmore Family]

I am getting the subject error when running a Python script called repeatedly 
from another script.

The snippet_ft8_rxtx.py shows the call, FT8_Receive.main(), in the while loop.
FT8_Receive.py shows the called script.
FT8_Receive.pdf is the flowgraph used to generate the called script which as 
you can see has been modified in main() and with check_time added.

The first call to the script is OK but the second call results in the error 
shown in audio_error.txt.

Why is the audio source busy when the flowgraph is stopped (or is it not 
stopped?) and how do I fix the issue?

Jim

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FT8_Receive.pdf
Description: Adobe PDF document

gr::log :ERROR: audio_alsa_source1 - [hw:1,0]: Device or resource busy
Traceback (most recent call last):
  File "/home/pi/gr-ft8_rxtx/python/ft8_rxtx.py", line 336, in <module>
    main()    
  File "/home/pi/gr-ft8_rxtx/python/ft8_rxtx.py", line 319, in main
    FT8_Receive.main()
  File "/home/pi/gr-ft8_rxtx/python/FT8_Receive.py", line 205, in main
    tb = top_block_cls()
  File "/home/pi/gr-ft8_rxtx/python/FT8_Receive.py", line 85, in __init__
    self.audio_source_0 = audio.source(samp_rate, 'hw:1,0', True)
RuntimeError: audio_alsa_source

FT8_Receive.py
Description: Binary data

snippet_ft8_rxtx.py
Description: Binary data