Well, I'm still struggling with this. As a fix, I've tried the server-side decompress, but still no joy:
"Connected to localhost, for user <username>, starting transfer...
Current directory is now: /httpdocs Files transfer finished!
Permissions restored to their initial value...
Files succesfully copied to httpdocs/ on localhost using FTP
Warning: fopen(/var/www/vhosts/<domain>/httpdocs//configuration.php) [function.fopen]: failed to open stream: Permission denied in /var/www/vhosts/<domain>/httpdocs/Joomla.Cloner.php on line 1461
Unable to write to configuration file /var/www/vhosts/<domain>/httpdocs//configuration.php... Aborting..."
I see a similar problem
here, but I don't yet have a configuration.php file on the server, so I can't change its permissions...
Any ideas for both this and the previous problem?