"You do not appear to have any plugins available at this time." Is the message in my Admin/Plugins despite having Akismet installed previously.
Anyway, I've used the "Add New" in the Admin/Plugins area and selected something like JetPak and despite saying success, etc when I "activate" I get this error, "The plugin does not have a valid header" in Firefox browser.
Note: This issue was opened a few months ago in another post and never resolved.
Note 2: I've tried uploading FTP and they do not show up in the Admin/Plugins area.
It is a standalone installation of the latest version of WordPress on Apache/CentOS.