I am unable to use the app store. After a recent update, it says that I must be connected to the internet, when I am. The only thing I can think of that might be causing this issue is that I have 3 NIC's in my machine due to using VM's. Can anyone please assist?
I had exactly the same problem.
The solution is in this post: 'no' internet connection within appcenter
Edit your /etc/network/interfaces and add the following:
auto eno1 iface eno1 inet dhcp
(eno1 might be eth0 or something else, its your Ethernet adapter name)
Then restart your network-manager:
sudo service network-manager restart
And it should work