TG100 Web Interface problem

I am having problems with my TG100 device (HW Version V2.20, firmware 51.18.12.51). Every 7-10 days, the web interface becomes inaccessible and prompts me to reset the config to factory default and/or update the firmware. While the device itself continues to operate normally and performs both incoming and outgoing calls, this issue is extremely frustrating as the device is installed at a remote location and it takes time for me to access it and reboot it.