This "Network Failed" notification comes directly from the Chrome browser and generally means a couple of different things:
- There may be a slow connection between the Chrome Web Store and your computer, which would case a timeout and the "Network Failed" error
- There may be security software installed on your computer preventing you from downloading a mail extension to your Chrome Browser.
If you can not install any other app on Chrome, we highly recommend to uninstall your Google Chrome browser and reinstall it.
More info available here: https://support.google.com/chrome/answer/2898334?hl=en#networkfailed