Thank you for the hint!
I did contact the host and the problem was not the ziparchive but rather that they had two types of ftp users, one of them specifically for wordpress…
I can now install themes and plugins beautifully, except that this particula plugin still does not work
by the way: I had problems before because the upload function could not find my wp-content directory. I fixed that by adding
define(‘FTP_USER’, ‘username’);
define(‘FTP_PASS’, ‘password’);
define(‘FTP_HOST’, ‘ftp.example.org’);
define(‘FTP_BASE’, ‘/path/to/wordpress/’);
define(‘FTP_CONTENT_DIR’, ‘/path/to/wordpress/wp-content/’);
define(‘FTP_PLUGIN_DIR ‘, ‘/path/to/wordpress/wp-content/plugins/’);
in the wp-config.php
just in case anyone has the other problem too..
