I've got an ASUS RT-N16 with Tomato Firmware v1.28.7505 MIPSR2Toastman-RT K26 USB VPN.
This router replaced a router a few weeks ago of the same model and same firmware. The device appears to run just fine for many days and then it will lock up and require a power cycle. The previous unit was doing the same thing. Today when this device locked up I went onsite and removed all the LAN connected enet cables and just connected my laptop to the LAN side. The device would not respond to a ping 192.168.1.1. I power cycled the unit and now it is working again. Via network management I had received an alert that the network was not reachable beginning at 9pm last night. I had had the router set to reboot at 4am daily but it appears that this did not happen today.
I am using same hardware and same firmware at other sites and not having this problem.
Can you suggest something more to correct or troubleshoot this problem?