Same problem here with two servers:
Plesk Onyx 17.5.3 Update #82 Debian 8.11 The panel can't be updated as I received the error described
Plesk 12.5.30 Update #79, Debian 8.4 The panel can't be updated as I received the error described
And I don't know what to do....
Plesk Onyx 17.5.3 Update #82 Debian 8.11 The panel can't be updated as I received the error described
Plesk 12.5.30 Update #79, Debian 8.4 The panel can't be updated as I received the error described
And I don't know what to do....