I keep getting "The feature you are trying to use is on a network resource that is unavailable. "
This application installs differently based on the browser used to visit the official website. That message indicates that the update resource is not found or is not accessible. In this case, you have a few options:
Remove the plugin and then visit the official website to install it again: http://www.getsidekick.com/email-tracking-outlook
Contact the developers and explain that the update package from their servers is not reachable: http://sales.hubspot.com/knowledge/sidekick-getting-started/article/how-to-update-sidekick
2.1 On the above page, there are also instructions on how to update the application.