Once I got my new Verizon CR1000A router (which replaced my MI424WR), I lost the ability to connect to my employer's VPN using Cisco AnyConnect via Ethernet (strangely I was able to connect to Cisco AnyConnect through Wifi, with the Ethernet jack completely unplugged, but, sadly, using Wifi is not acceptable with my employer).
On Ethernet, I was getting the error "Connection attempt has failed due to server communication errors. Please retry the connection"
Eventually, I was able to log into the CR1000A router using my cell phone (which was connected to the router by Wifi) and the credentials on the back of the router ("mynetworksettings.com" and the password), and then clicking "Advanced", "Network Settings", "IPv6", and sliding the "Enable IPv6 Support" slider to the left (and clicking "Apply Changes") to disable IPv6. Then, I rebooted my computer, and retried connecting the VPN. The error message disappeared, and I was able to sucessfully connect to Cisco AnyConnect via Ethernet.