Create an Easy VPN server by entering a Tunnel Name. That name must not have a space in it (undocumented it seems, didn't work for me with a space in that name). Then enter a password. I used full tunnel mode and create a user and put it in the All Users group.
On the client I installed Cisco VPN Client and created a new profile. Give it any name you like and optionally a description. Use Group Authentication and as Name you select the Tunnel Name. As Password you enter the password. Enter the host (the WAN ip of the router), click Save and connect. Enter the username and user password and you should be running. If not, something may be blocking the VPN connection.