You will get this error if you try to install it on your own PC. Many of the plugins are meant to install on your PC, but this particular one is meant to be installed on the publisher CallManager itself. Make sure you are on the console of the machine or using VNC to connect to the console, and then use a web browser on the publisher itself to download and run the plugin.
If you are getting this error while trying to install on the publisher, please let us know.
