This message appears on the Showcase Workshop app when the tablet or device has WiFi or mobile data turned on, but the internet is not properly connected - e.g. there is a problem with the service, or a poor quality data connection. A message like this is not coming from a problem the Showcase app.
Although showcases can be viewed offline, a working internet connection is needed to sign in and download showcases.
You can always try the ol' "turn WiFi off/on again"; or, you can connect to a different WiFi connection and try again.
Note that if you're seeing this message on an app other than Showcase Workshop, we unfortunately can't help you - sorry about that!