Recently had this problem with our C120 circa 2006 unit. We shut the unit down, pulled the CF card and the reboot cycle stopped. The first time this happened was just as we started to cross the Columbia Bar on our way up to the Gulf Islands last month. Needless to say we lost all use of it and autopilot/speed/depth until we got to Westport where we worked on it and found the card was bad. We swapped to our Canadian CF card and it behaved normally again. It has now worked for a month without issues. FYI, we already have the latest Raymarine firmware for our unit. Hope your fix is as simple!