I'm a Google Play Music user running Rhythmbox 2.99.1 on Ubuntu 13.10.
Recently, I found a link to a Google Play Music Plugin that had instructions on how to install the plugin.
After following these instructions, I opened up the Rhythmbox Plugin Window, and checked the Google Play Music box. Then a red minus appears to the left of the plugin.
After this error appears, no changes are made to the program.
How can I get this plugin to work properly on my system?