This problem is due to the Vodafone Station that automatically redirects any requests on port 80 icoming from new MAC addresses.
To solve this problem open a browser on a PC wired on the same LAN and go to the following URL changing ff:ff:ff:ff:ff:ff with the MAC address of your Acme board:
Then click on the top-right X to close the page and confirm on the next page.
Now try again with apt-get command on your Acme board.