This suggests problems with the validation of the SSL certificate of the remote (moodle.org) site.
This is also a known problem in Moodle Windows 7 servers running the Moodle package for Windows.
The web server process has to have write access to the plugin type folder where the new plugin is to be installed in order to use either of these methods.
Any updates available are highlighted, with further information and a download link in the notes column opposite the plugin.
An administrator can enable updates deployment in Administration Update notifications.
If you can't deploy the plugin code via the administration web interface, you have to copy it to the server file system manually (e.g.
if the web server process does not have write access to the Moodle installation tree to do this for you).
This is however improving over time with the evolving new plugins directory system. There are three ways how the plugin code can be deployed into Moodle.