Problem loading media_player_mpy item into trial sequence

Hi, I'm new to OpenSesame, having recently switched over from E-Prime. I'm setting up the skeleton of an RT experiment but can't get OpenSesame to allow the dragging of an media_player_mpy item into my trial sequence. I'm running version 3.1.6 so already have the required plug in. I'm guessing this issue is specific to the fact I am a Mac user (OS El Capitan 10.11.6)? The entire error message is pasted below.
Would appreciate any help on this - even it is confirmation that I can't continue with this combo of soft and hardware......

--K

Error message:

Traceback (most recent call last):
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/libqtopensesame/widgets/tree_overview.py", line 753, in dropEvent
self.drop_event_item_new(data, e)
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/libqtopensesame/widgets/tree_overview.py", line 672, in drop_event_item_new
item, new_items = self.drop_get_item_snippet(data)
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/libqtopensesame/widgets/tree_overview.py", line 560, in drop_get_item_snippet
catch_exceptions=False)
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/libqtopensesame/misc/qtitem_store.py", line 105, in new
script=script)
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/libopensesame/item_store.py", line 164, in new
u"Failed to load plugin '%s'" % _type, exception=e)
osexception:
Failed to load plugin 'media_player_mpy'

item-stack:
exception message: Unable to download 'ffmpeg.osx'. Perhaps there is a no internet connection? If there is, please report this problem.
time: Wed Mar 29 10:05:40 2017
exception type: IOError

Traceback:
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/libopensesame/item_store.py", line 161, in new
self.experiment, script, self.experiment.item_prefix())
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/libopensesame/plugins.py", line 360, in load_plugin
item_module = import_plugin(plugin, _type=_type)
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/libopensesame/plugins.py", line 331, in import_plugin
return imp.load_source(plugin, path)
File "/Applications/OpenSesame.app/Contents/Resources/share/opensesame_plugins/media_player_mpy/media_player_mpy.py", line 42, in
import mediadecoder
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/mediadecoder/init.py", line 6, in
from mediadecoder.decoder import Decoder
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/mediadecoder/decoder.py", line 9, in
from moviepy.video.io.VideoFileClip import VideoFileClip
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/moviepy/video/io/VideoFileClip.py", line 3, in
from moviepy.video.VideoClip import VideoClip
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/moviepy/video/VideoClip.py", line 20, in
from .io.ffmpeg_writer import ffmpeg_write_image, ffmpeg_write_video
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/moviepy/video/io/ffmpeg_writer.py", line 15, in
from moviepy.config import get_setting
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/moviepy/config.py", line 38, in
FFMPEG_BINARY = get_exe()
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/imageio/plugins/ffmpeg.py", line 52, in get_exe
exe = get_remote_file('ffmpeg/' + FNAME_PER_PLATFORM[plat])
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/imageio/core/fetching.py", line 98, in get_remote_file
_fetch_file(url, filename)
File "/Applications/OpenSesame.app/Contents/Resources/lib/python2.7/site-packages/imageio/core/fetching.py", line 154, in _fetch_file
os.path.basename(file_name))
IOError: Unable to download 'ffmpeg.osx'. Perhaps there is a no internet connection? If there is, please report this problem.