It is serial communication error while system is executing after powersupply on. Following reasons can be considered.1) Optical cable connection is fault or cable is not connected or cableis cut.2) MAIN CPU board or option 2 board is fault.3) Spindle amp. printed board is fault.If this alarm occurs when CNC power supply is turned on or whenthis alarm can not be cleared even if CNC is reset, turn off the powersupply also turn off the power supply in spindle side.