More often than not, this notification appears if the internet signal strength is poor.
The first thing to do is to check the light status on your hub. The WiFi symbol should be flashing amber.
If the WiFi symbol on the hub isn't flashing amber, unplug the Ethernet cable from your broadband router and switch it over to a different port and wait 5-10 minutes.
If the above suggestion doesn't work, the next step is to power cycle the hub and the broadband router (switch it off and on again).