Make sure the file is indeed in this location by running ls on it in a terminal:
~$: ls /media/lab70809/Data01/speech_donoiser_new/datasets/ner-300hr/cv/mix/BG_20170420_133-JZ_20160301_040_LTL7zFtz8UQ_snr6_fileid_528.wav

of this returns valid file information, I would guess that the mount is somehow dropped during the script execution.