When accessing the internet on tablet the `Unfortunately, internet has stopped` message appears even though it is showing that wifi is connected

Verify that your router has a good internet connection and that its local IP service (usually through DHCP) is running. Try entering the router's TCP/IP address (e. g., http://169.168.1.1) in your browser's address bar to see if you can get the router's status page.

One of the more common failures in older routers is IP service dropout, particularly if the router overheats because something was stacked on top of it. This will result in client error messages such as the one you describe.

Another possibility is an authentication failure, but that would generally mean somebody messed with the wireless network access password, or there's a bug in the wireless coding (as in some ASUS laptops - this was fixed in a firmware update).