All user plugins won't install ...

When kiwidude released the last update for Quality check - I (as usual) went to get it, but an error was returned:

calibre, version 0.8.55
ERROR: Unhandled exception: <b>error</b>:[Errno 10054] An existing connection was forcibly closed by the remote host

Traceback (most recent call last):
File "site-packages\calibre\gui2\dialogs\plugin_updater.py", line 718, in _install_clicked
File "site-packages\calibre\gui2\dialogs\plugin_updater.py", line 869, in _download_zip
File "site-packages\mechanize-0.2.4-py2.7.egg\mechanize\_response.py", line 190, in read
File "socket.py", line 351, in read
File "httplib.py", line 561, in read
File "socket.py", line 380, in read
error: [Errno 10054] An existing connection was forcibly closed by the remote host

I uninstalled and reinstalled Calibre (using Revo) tried again, and got the same message. Then out of the blue, I was able to install three of kiwidude's plugins I always use, but when I tried to install a fourth (Manage Series) I got the error again. When I closed the plugin GUI and "applied" the changes - none of the three successful installs had taken on the toolbar. So I am still pluginless and frustrated! :)

I then went back and tried a random plugin from another developer but got the same thing.

Any suggestions??