Unable to reach plugin index page

Just updated to 5.20/64bit. Seemed to go ok, until I checked for updated plugins.
Message "Unable to reach the plugin index page"
Also tried Get New Plugins - same message.
Calibre was installed in the same directory as before, if that matters:
F:\Program Files (x86)\Calibre2

using Windows 10.

Any suggestions?? thx,


Follows copy of details:
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calibre, version 5.20.0
ERROR: Update Check Failed: Unable to reach the plugin index page.

Traceback (most recent call last):
File "calibre\gui2\dialogs\plugin_updater.py", line 435, in __init__
File "calibre\gui2\dialogs\plugin_updater.py", line 69, in read_available_plugins
ImportError: DLL load failed while importing bz2: %1 is not a valid Win32 application.


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