I just enabled unit failover and now I cannot get back in to the FatPipe device.
By design when unit failover is enabled, if there is not a link on the LAN interface and at least one WAN interface the FatPipe will go into a down state and will not have it's interface IP addresses loaded. In order to access the Fatpipe by its configuration's IP address make sure that there is link on the LAN and at least one WAN interface. A simple method of gaining access to the FatPipe via its IP Address is to Plug into the LAN port with a computer, and link the WAN1 and WAN2 interfaces together with a straight-through or crossover cable.
Also note that when unit failover is enabled the MAC addresses of the interfaces will change, this ensures a seamless failover from one device to the other as it will not require an ARP table change, since both device(s) sets of MAC Addresses will be identical assuming the same Group ID was set in the Unit Failover configuration page.