Spam Karma won’t install

I tried the 1-click install of several plugins using the latest WP Plugin Manager ( 1.6.4.b) but it does not seem to work. I get the message “This package does not contain a plugin file (might be a standalone script)” on an orange background, and there is no plugin file in my plugin directory. I tried with Spam Karma, Adhesive, Spammer TarPit, and a few others, all with the same result.

The permissions on the directories appear to be set and reset properly, and WPPM seems to think that the plugins are installed, because it lists them as such, yet the admin plugin control panel does not show them, and they are nowhere to be found in the directory tree.

Pierre