if debug is activated you should have *much* more than this in your log file.
It should list any plugins that have not been able to load etc. and if you installed the plugins via an updatesite (i.e. dont just unzip the the zip) it gotta show up here if it does not show up in the UI.
btw. you did see this from the installation guide, right:
Download an Update Site Zip, but DO NOT UNZIP IT.
and then we continue showing how to use the Update Manager to install it ?