Error decoding file when generating am,fm and amssb mod. 

When I excecuted 'python generate_RML2016.10a.py', errors occurred when generating am, fm and amssb mod:

[mp3 @ 0x7f8130000c60] Skipping 0 bytes of junk at 70700.
[mp3 @ 0x7f8130006380] Header missing
error decoding file

I think the my gnuradio 3.7 config is probably not right. How to deal with this?
Thanks!