Plugin install failed

Unable to install the cms2cms-joomla-to-wp-migration plugin, tried it by unzipping it in the wp-content/plugins dir, and the ftp way, that gave me the output:
……………………………………………….
Installing Plugin from uploaded file: cms2cms-joomla-to-wp-migration.3.1.0.zip
Unpacking the package…

Installing the plugin…

The package could not be installed. No valid plugins were found.

Plugin install failed.

Return to Plugins page
……………………………………………….

Enabling wp_debugging also did not work:
define(‘WP_DEBUG’, true);

// Enable Debug logging to the /wp-content/debug.log file
define(‘WP_DEBUG_LOG’, true);

But the wp-content/debug.log is empty

What goes wrong?
Thanks in advance

http://wordpress.org/plugins/cms2cms-joomla-to-wp-migration/